why would you use std_logic_vectors - they are not numbers - what a pain in the arse to do all the type conversions.
I suspect this is homework. I suggest having a go yourself, and asking specific questions, rather than "I dont understand, please do my homework for me".
Well, I've made my matrices to multiply. I have no idea how to add to accumulate (register?) and make it parallel and pipelined.
The parallel and pipeline thing confuses me, because now I don't think I made the matrices correctly since I only made it to multiply with an output of 4x3