Every checked round comes down to three values: a server seed, a client seed, and a nonce. If you cannot name which one you control, you are not reading anything.
The server seed belongs to the site. Before you play, you should see it as a hash, a long string that seals the value without showing it. The client seed is yours. Set it yourself, or the default the site picked is doing the talking for you. The nonce is a counter. It climbs by one each round so the same two seeds never repeat a result.
Together they produce the outcome: server seed plus client seed plus nonce, run through a published formula. Change any one of them and the result changes.
When a round ends, the site should reveal the server seed. Hash that reveal yourself and compare it to the hash you saw before you staked. If they match, the seed was fixed before you clicked. Then rerun the formula with your client seed and the round nonce. The number you get should be the number you were shown.
If the reveal never comes, or the hash does not match, the check does not exist. You are back to trusting the house.
If the site will not reveal the seed, there is nothing to read.
If you would like to learn more about the technical workings of provably fair algorithms, you can download the whitepaper.