Help: How can black win here?

hello guys,i have been analysing my games and when i came to this position. I couldn't understand it so used a chess engine to evaluate this position:

it is black to move, the computer evaluates -7.00 which is certainly black is winning but i don't know how to play and win in the position.Any ideas/suggestion on how should black win here? any ideas are appreciated. thanks in advance.

Hi brod Alcausin.

Rb8 followed by Bb7?

Yup, Rb1 followed by Bb2 and c4 wins a piece or you can harvest the pawn with Nb6.

thanks for your suggestions

I think Rb1 is not that solid, because 1.Rb1 Kh2 and c1 is supported by Rh1 and Nb3. May be black is winning because of the pawn advantage.