With On the Clock you make the picks for your team, but the other 31 teams are autopicked for you. The simulator is based on a combination of the current big board rankings and the current team needs, which will be updated throughout the draft process.
Instead of having the draft set to the standard drafting schools of thought of best player available (BPA) or drafting by team need, the simulator tries to combine the two, for a more realistic experience. There is a variability to ensure that the drafts don't come out the same each time, so you should try to draft multiple times to see what is the best overall draft you can come up with.
So enjoy the draft and see what is the best draft you can have for your favorite teams!