how to read analysis ?

All you should be using an engine for is to check for blunders and missed tactics. 

All that + and - crap will do you no good right now.

But to give you a quick answer:

+ means advantage white.

- means advantage black.

+.33 means white is better by 1/3 of a pawn.

-.5 means black is better by 1/2 a pawn.

Is there a legend available 

Im sure somewhere there is, but i dont know

Yea the engine evaluates a position based on centipawns, which @IMBacon described with examples

https://support.chess.com/category/171-analysis

https://support.chess.com/article/656-what-do-the-computer-evaluation-numbers-mean-like-225

the first step is to completely ignore the computer evaluations.

the second is to find human evaluations. Perhaps the best, most complete set of symbols for evaluation is used by Chess Informant. you can find summaries here and here