Most yards have outdoor hoses and water spigots. But for people who spent a lot of times outdoors and do a lot of gardening chores, an outdoor sink can provide efficiency and convenience. An outdoor sink gives gardeners a place to rinse out pots, wash hands and do general cleanup before going into the house. To add an outdoor sink to your home, simply follow a few basic steps. 
Instructions of adding an outdoor sinks step by step as follows, and I believe you will benefit much from them.
Firstly, identify your water hookups outdoors. You may have cold water only, or both hot and cold. Also, identify the drain to which you will be hooking up your sink.
Secondly, buy a sink and base cabinet, available at any major hardware store. For outdoor sinks, stainless steel is your best choice because of its durability. Place the base cabinet into proper position against the water hookups.
Thirdly, shut off the waterline that runs to the sink. Connect the water hookups to the matching sink fittings. Use a wrench and Teflon paste to ensure a tight fit.
Fourthly, install your outdoor sink's drain. Use silicon caulk around the drain hole and connect the drain to the sink by threading the two tightly together.
Fifthly, lay a bead of silicon caulk around the perimeter of the base cabinet's opening. Place the sink into position and press firmly. Make sure the sink is seated properly and doesn't move.
Sixthly, turn the main waterline back on. Turn on the water to the kitchen sink. Observe if there are any leaks and that the sink's drain is functioning properly.
Tips & Warnings
Consider using a grill cover to cover the sink and the top of the sink cabinet to protect it from the elements and from animals.

Test the sink each spring to make sure it doesn't leak. If you live in cold climates, shut off water to the sink during the winter.