The Additions to Daniel comprise three chapters not found in the Hebrew/Aramaic text of Daniel. The text of these chapters is found in the Greek Septuagint and in the earlier Old Greek translation. They are accepted as canonical and translated as such in Roman Catholic, Eastern Orthodox and Oriental Orthodox Bibles. They are listed in Article VI of the Thirty-Nine Articles of the Church of England. However, most Protestant Versions exclude these passages as apocryphal, retaining only the text available today in the Hebrew/Aramaic manuscripts.

The additions are: The Prayer of Azariah and Song of the Three Holy Children : Daniel 3:24-90 inserted between verses 23 and 24 (v. 24 becomes v. 91) in the Protestant cannon. It incorporates the Fiery Furnace episode.
Susanna and the Elders : before Daniel 1:1, a prologue in early Greek manuscripts; chapter 13 in the Vulgate.
Bel and the Dragon : after Daniel 12:13 in Greek, an epilogue; chapter 14 in the Vulgate. (Summary by Wikipedia)