I dont know how to loop in crocheting?

i know the basics of crocheting, but i havent tried a pattern before and in one of the rows it says "ch 5 (which i know what that means), sc in ch 5 lp. i dont know how to loop. and what it means to sc in ch 5 lp. i know the abbreviations and how to do them but i dont know how to put them together