Most dishwashers rinse first. They do a short cycle with just water. It removes the big debris, helps prevent redepositing of debris, and if your machine has an "auto" or "sensing" mode, its using the rinse water to determine how dirty the dishes are and what cycle it needs to run them at.

Soap isnt dispensed until after this for the wash cycle.

Pro-tip: a better pre-wash cycle can be obtained by running your sink faucet hot water until it comes out hot, so the initial rinse cycle is hotter. You can also sprinkle some powdered detergent in the rinse tub when you start to get a more powerful preclean.