So I'm basically new to bikes. I've been riding them my whole life but just recently got a hand-me-down mountain bike, and am using it for everything.

My problem is i don't know what the previous owner did with it or how to even go about correcting it. When i get it into the lowest gear (after going through the previous ones to get up to speed) if i crank too hard the chain will start to skip. This morning i tried moving the wheel further back while in the low gear to stretch the chain but it didn't really move much.

I would appreciate any help as I'm new to bikes and this forum. Though I've been reading around here for a while and its great.