Im new at fishing and i need some help. Ok i have a shakespeare medium heavy action 8-15lb line with a spinnercast on it. Now my questions are: what size line do i use for rod? I want my line to go far when i cast out how do i accomplish that? Explain the weights to me in dummy terms lol. I had put a heavier line on a old rod i was given and it didnt cast out far at all. Please help me out thanks.

Welcome to the forum!  Line weight is a give and take kinda deal.  The higher the poundage the more abrasion resistant it is, but you lose casting distance and lure action as you go up.  So you have to find a balance between good enough casting distance and strong enough to fish where you want to fish.

 

For that setup with a spincast, I would recommend 10-12 lb Berkeley Trilene XL or McCoy mean green.  Both of these are very supple so they should cast well out of a spincast.  The McCoy is probably a little more abrasion resistant.