Comes with 2 washers, a skinny washer lays in the bottom at all times inside the faucet adapter (kitchen sinks) and sometimes you will use the fat washer on top of the skinny washer (bathroom sinks)
To use remove the areator from the sink, use a towel with pliers to make sure you do not scrape off the customers chrome finish off the areator. Run the water for a bit to get the correct water temperature you want to use. Turn water back off. Hand tighten the installation of the faucet adapter while using the correct washers, then back twist the garden hose and hand tighten the garden hose connection to the faucet adapter. Turn on the water supply on to test water for leaks. The reason for back twisting the garden hose is so when you turn on the water pressure, the garden hose tightens the water connection and not loosens it. In most cases you will not need to do anything else but in a few rear cases you might have to drape a rag over the top of the connection to make sure any leaks drip back into the sink.
It is a good idea to have a few extra areators on hand to sell to customer that have super clogged or old ones.