Does characteristics and main idea means same??

No. A characteristic is something you possess like she is smart, he is witty, you laugh everyday, he is kind, they are determined, she is passionate.

A main idea is more of writing term as in "What is the main idea in your paper?" If you were asked that about a paper about The Renaissance

You would say, "The Renaissance."

Or go in more depth like, "The main idea is the Renaissance I transition into from the Dark Ages and go into depth about the writers, artists, and musicians."

Explanation:

Hope this helps!