When a normal file becomes an nft, it needs to be stored on the same blockchain as the desired collection. This could be anything ranging from your digital identity docs to a bunch of jpegs that are pumped by marketing schemes.
The mint happens when the normal document get consumed by the blockchain and thus tokenized. It now has a unique identifier on the blockchain that can never be edited. The chain from this point on can only add data to the nft's story, but not erase or edit it.
Yo, I didn't realize I was apeing in last night until I checked Opensea this morning. Luckily I didn't get hacked, but dang minting was so easy!