Heres a simple picture of a double sink hookup. The tee that connects to two sink waste lines can be in the center or under one side with the other line tying into the side inlet of the tee. The dishwasher tee is usually 1-1/2" with a smaller inlet on an angle to promote drainage. You need to know what size your DW needs for the drain.
If you have never made a mistake, you haven't done much.