How Long can beer stay in a gl bottle?

I bought a home brewing beer kit. All it comes with is the plastic amber bottles. I know it can not stay in there long because of the plastic. I bought clear gallon jugs for my beer instead because the amber gl jugs are expensive for me. How long can I keep my beer in the clear jugs and if not for long can I use something to cover the jugs to protect against light damage? Like tin foil or something?