In the fancier onsens, you’ll find bathing stations with a faucet, showerhead, and stool to sit on. Some will even have soap and shampoo. You can sit on the stool and bathe much like you would at home — except you’ll want to turn off the water while you soap up or shave.
In a more basic onsen, you’ll find just a stack of plastic or wooden buckets. If there's no faucet, dip the bucket into the onsen and use it to get yourself wet. Be careful not to splash your neighbors.