This is thanigai... what do the word "MESSIAH" mean? I want a clear and brief answer...

... what is the difference between the two testaments of bible...

The Old Testament is simply a history of the Hebrew people. The New Testament tells of the birth, life, death and teachings of Jesus. It then tells of various disciples' ministries, and the ministry of Paul to the gentiles (non-Jews) of Europe, the Middle East and Asia. Finally, the book of Revelation deals with the past, present and future events. This is very general. There is so much more.

From Greek, from Aramaic məšiḥā, the anointed one (from məšaḥ, to anoint), or Hebrew māšîaḥ, anointed (from māšaḥ, to anoint).]
In the Old Testament the Messiah is referred to as the Anointed One.