The NT is normally divided into four main parts (Gospels, Acts, Letters, Apocalypse),
although the twenty-one "Letters" are best subdivided into three different sub-categories:

I) Four "Gospels": "Good News" about Jesus Christ; authorship attributed to the four "Evangelists"; verbal portraits of Jesus written for various early Christian communities; similar to ancient biographies in form (but rather different from modern biographies!):

The Synoptic Gospels:
          Matthew  (28 / 1071 / 18345)
          Mark  (16 / 678 / 11304)
          Luke  (24 / 1151 / 19482)

The Fourth Gospel:
          John  (21 / 879 / 15635)

II) One "Acts": a partial narrative account of the growth of the Early Church; a continuation of Luke's Gospel; contains historical materials, but is not a complete "history" of apostolic Christianity (at least not by modern historical standards):

The Acts of the Apostles  (28 / 1005 / 18451)

III) Twenty-One "Letters" or "Epistles": written by (or attributed to) various early Christian leaders, known as “apostles”

IIIa) Thirteen Letters attributed to Paul: real letters written by Paul (or his associates) to particular communities or individuals, concerning various local problems and issues:

Letters sent to Christian communities in the following cities:
          Romans  (16 / 433 / 7111)
          1 Corinthians  (16 / 437 / 6829)
          2 Corinthians  (13 / 256 / 4477)
          Galatians  (6 / 149 / 2230)
          Ephesians  (6 / 155 / 2422)
          Philippians  (4 / 104 / 1629)
          Colossians  (4 / 95 / 1582)
          1 Thessalonians  (5 / 89 / 1481)
          2 Thessalonians  (3 / 47 / 823)

Letters addressed to individual Christian leaders:
          1 Timothy  (6 / 113 / 1591)
          2 Timothy  (4 / 83 / 1238)
          Titus  (3 / 46 / 659)
          Philemon  (1 / 25 / 335)

Notes on the Pauline Letters:
* 1 Tim, 2 Tim, Titus are usually called the "Pastoral Letters" since they are addressed to leaders or "shepherds" of Christian communities.
* Phil, Phlm, Col are sometimes called "Prison Letters" since Paul evidently wrote them while in prison (Phil 1:7,13-14; Phlm 9-10; Col 4:3,10).
* Rom, 1 Cor, 2 Cor, Gal, Phil, 1Thess, Phlm are often called the "Undisputed Letters," since most scholars agree they were written by Paul himself.
* Eph, Col, 2 Thess, and 1 Tim, 2 Tim, Titus are often called the "Disputed" or "Deuteropauline Letters," since many scholars believe they were written by Paul's followers after his death, rather than by Paul himself.

IIIb) One Biblical Sermon: interprets Jesus in light of the OT; in the past sometimes attributed to Paul, but neither the author nor the audience is explicitly mentioned:

Hebrews  (13 / 303 / 4953)

IIIc) Seven Catholic Epistles or General Letters: authorship attributed to other apostles (for whom they are named!); most not written to individual communities, but to broader audiences ("catholic" = "general, universal"):

James  (5 / 108 / 1742)
1 Peter  (5 / 105 / 1684)
2 Peter  (3 / 61 / 1099)
1 John  (5 / 105 / 2141)
2 John  (1 / 13 / 245)
3 John  (1 / 15 / 219)
Jude  (1 / 25 / 461)

IV) One "Apocalypse": a highly symbolic narrative that interprets a historical crisis and provides hope for a better future:

The Book of Revelation  (22 / 404 / 9825)

 
For more information on all the above, please see my Biblical Glossary.

1. The 27 books of the New Testament are NOT listed in chronological order (the order in which they were written historically); several other principles were operative.
2. The overall order begins with the life of Jesus (four Gospels), then deals with the beginnings and expansion of the Church (Acts), then addresses particular issues and problems in early Christianity (Letters, Epistles), and finally focuses on the Eschaton or "End Times" (as described symbolically in the Book of Revelation).
3. The four Gospels are listed in what was traditionally regarded as their chronological order (i.e., Matthew was thought to be the oldest Gospel); most scholars today, however, believe that Mark was the first written Gospel (or at least the oldest of the four canonical Gospels in their full versions, as we know them today).
4. The Acts of the Apostles was originally the second volume of Luke's two-volume work; but when the four Gospels were grouped together, Acts was placed after John.
5. The Pauline Letters (written by, or at least attributed to Paul) are divided into two sub-groups: those written to communities and those addressed to individuals; within each sub-group, the letters are arranged not in chronological order, but rather in decreasing order of length (more or less, although Galatians is slightly shorter than Ephesians).
6. The anonymous "Letter to the Hebrews" comes immediately after the Pauline letters because people used to think it too was written by Paul; it may have been written by one of his followers, but was almost certainly not written by Paul himself.
7. The Catholic or General Epistles are also listed in decreasing order of length, although letters attributed to the same apostle are grouped together.
8. The Book of Revelation (singular! not "Revelations"!) closes out the NT canon, since it concludes with a description of the end of time (New Heavens, New Earth, New Jerusalem, etc.).

1. The Historical Jesus - words are spoken and deeds are performed by Jesus himself during his lifetime on earth.
2. Oral Tradition - traditions and beliefs about Jesus are developed and passed on by early Christian communities.
3. Written Sources - some of the miracles and/or sayings of Jesus are compiled and recorded in early written documents.
4. Written Texts - individual letters, full Gospels, etc., are written with particular messages for particular situations.
5. Distribution - some writings are copied and shared with other Christian communities throughout the Mediterranean.
6. Collection - certain Christians begin collecting the letters of Paul and gathering together several different Gospels.
7. Canonization - four Gospels, several collections of letters, and a few other texts are accepted as authoritative scriptures.
8. Translation - biblical texts are translated into ever more ancient and modern languages:  Latin, Syriac, Coptic, Armenian, etc.
9. Interpretation - the meaning of the scriptures is investigated on various levels:  literal, spiritual, historical, social, etc.
10. Application - communities and individuals use the NT for practical purposes:  liturgical, moral, sacramental, theological, etc.

1. Apostolic Origin - attributed to and/or based on the preaching/teaching of the first-generation apostles (or their closest companions).
2. Universal Acceptance - acknowledged by all major Christian communities in the Mediterranean world (by the end of the fourth century).
3. Liturgical Use - read publicly along with the OT when early Christians gathered for the Lord's Supper (their weekly worship services).
4. Consistent Message - containing theological ideas compatible with other accepted Christian writings (incl. the divinity and humanity Jesus).

1. Selectors - from among the many things Jesus said and did, they chose which stories they wanted to include and which to omit.
2. Arrangers - they organized the materials in a particular sequence, not necessarily chronologically but often in thematic blocks.
3. Shapers - they adapted and edited the individual stories from their sources so as to emphasize the themes they wanted to stress.
4. Proclaimers - they were not objective historians, but preached the "good news" about Jesus in ways appropriate to their audiences.