For the voter who just wants to vote and leaves it to others to do any auditing, they simply take their ballot into the booth and fill in the bubble next to the option they want to vote for. It looks just like normal optical scan voting except filling the oval with the provided pen reveals a code instead of completely blackening the oval.
For the voter who wants to check later that their vote was included correctly in the total they have to also to note the codes that are revealed when they fill the bubbles.
Voters that wish to check that the have not received a rigged ballot can ask for two ballots, and then pick one of the two at random and reveal all the codes before going into the booth and using the other to actually vote with. They can afterwards look up all the codes on that first valid to verify they are all valid. This actually just shows that the ballot they picked to verify with instead of vote with was not rigged, but someone trying to slip in rigged ballots has a 50/50 chance of being caught each time a voter asks to do such a check.
https://en.wikipedia.org/wiki/Scantegrity looks sort of complicated.