IsleOfWight wrote Sorry if I sound stupid but how does it work? I want to do it with someone to trade games but I don't understand it?

I know you have to switch accounts but do you have to keep the other persons' account after you've downloaded it?

Can anyone explain it? Thanks in advance!

You don't need to keep the persons account, it's just a matter of making your xbox that accounts home. Once you do that, all the digital content that was purchased with that account will be available for you to use. It's only with games that have been purchased through the Xbox Store. Discs and game codes won't work.