A commitment scheme is a sealed envelope. The site shows you the seal before the round and opens the envelope after. That is the whole idea, and you can use it without reading a textbook.
Before you play, the site publishes a hash of its server seed. A hash is a one-way stamp: the same seed always makes the same stamp, but you cannot work backwards from stamp to seed. After the round, the site reveals the seed. You stamp it yourself. If your stamp matches the one from before the round, the seed never changed. It was committed before you clicked.
Copy the hash shown before you play and keep it. After the round, take the revealed seed, run it through the same hash function, any free tool will do, and compare. Matching stamps mean the site could not swap its seed after seeing your bet. That is the commitment doing its job.
The client seed and nonce then let you re-run the result itself. Commitment proves the seed was fixed; the full formula proves the outcome followed from it.
The seal is only useful if you saw it before the round. Screenshot the hash.
If you would like to learn more about the technical workings of provably fair algorithms, you can download the whitepaper.