"Borrow" means "to take (something, money) temporarily with the intention of returning it".
"Lend" means "to give (someone) the use of for a time".
In formal usage (especially in British English), lend is a verb and loan is a noun. However, the verb loan is considered acceptable when it concerns the lending of money.
Ex-"Borrow trouble for yourself, if that's your nature, but don't lend it to your neighbors." (Rudyard Kipling).