What is the difference between LORD and GOD? I need to understand whether GOD and LORD is the same or different.
The all upper-case "LORD" and "GOD" are used where the original Hebrew used the sacred name of god, YHWH (יהוה).

Traditionally, that four letter name (Tetragrammaton) is not supposed to be pronounced except by the high priests on the Day of Atonement.

To avoid accidentally saying it while reading the Hebrew scriptures, incorrect vowel marks are added to the word, specifically the vowels from "Adonai", meaning "lord".  Anyone reading it would know to say "Lord" at that point.

This article, "Why Does the Old Testament Sometimes Capitalize Lord or God?", includes a summary of the general rules that apply:


  
  When you see LORD, the specific name YHWH is used and it always
  refers to Him.
  When you see lord, the word adonai is used in such a way as to
      refer to a human master or lord.
  When you see Lord, the word adonai is used to refer to the
      true God.
  When you see God, the Hebrew words elohim, el, or eloah
  are used to refer to the one true God.
  When you see god or gods, the Hebrew words elohim, el,
  or eloah are used to refer to idols, spiritual beings, the objects
  of other nations’ worship, etc.
  When you see Lord GOD, the author has used both adonai and
  YHWH together.
  


So, to answer the original question, there is no real difference between "LORD" and "GOD":


"LORD" means that "YHWH" is supposed to be said as "lord".
"Lord GOD" means that "YHWH" is supposed to be said as "god" (otherwise the first rule would suggest saying "lord lord").