Note: I swear that I thought that this one had been covered here, but I did a search and couldn't find it. Spiff, if I'm going nuts, please feel free to merge.
Pretty simple: Go to store (A fair amount of supermarkets, drug stores, Walmart/Target, etc., participate.) and buy a participating item listed on the app. Scan receipt, get back money. You also get money for reading a trivia question about the item.
There's a sign-up bonus for both referree and referral. To get the bonus, you need to download the app, sign up and then sign in on your smartphone. Don't forget to actually sign in!
They've got a pretty crazy referral program going on right now (100,000 referrals gets you $150,000. Good luck with that, although I'm trying.).
Here I am:
https://ibotta.com/register?friend=b3CkTw
Mike