From their web site:
How Checkout 51 works
Browse your offers and buy products at any store.
Upload your receipt using Checkout 51.
We'll confirm your purchase and credit your account.
When your account balance reaches $20, you can cash out and we'll mail you a check.
Offers go live on Thursdays at 12:00 AM in each time zone. They expire the following Wednesday at 11:59 PM in each time zone. You must upload your receipts while the offers are live.
Offers are available in limited quantities. Please check your offer list before you go shopping to ensure that the offer is still available, and upload the receipt immediately after purchase to avoid disappointment.
Some offers may be claimed multiple times. Tap into the offer to see its claim limit.
Each receipt can only be used once.
You can only earn Cash Back for the exact product listed, so please read carefully.
You can earn Checkout 51 Cash Back in combination with any other coupon or discount unless otherwise stated. Tap into the offer to see any conditions.
Items purchased from online retailers are eligible for Cash Back. Itemized packing slips are accepted as proof of purchase. Online purchases are subject to the same upload timelines as receipts.
It's a great program, lots of variety and different items - and seeing as it takes less than a minute to submit your receipt - definitely worth it!
Click HERE to visit their site and join!