another need mentor post
Look at the lessons on those openings.
Look at explorer and grandmaster games where those openings were used.
Play a few and see what happens - what the strengths and weaknesses are.
French defence as black: strength is your opponent's pawn on d4 can be weak and needs defending. Weakness is trapping in the king's bishop.
Here is a game using that opening:
https://www.chess.com/games/view/13502337