Know your valve type: You need to know your tube's valve type to ensure that you purchase the correct tubes as replacements. And, so you know how to set up your pump, how to attach the pump to the valve and inflate the tire.
To add or let air out of Presta valves, you must first unscrew the tip by turning it counterclockwise. To let air out, press down on the tip, which opens the valve. Also, before inflation, press down to make sure the valve is open.
For Schrader valves, to release air, press something into the valve to depress the valve core (the little pin inside the valve). To inflate, simply attach the pump and get to work.
Presta valves are also called "French" and "needle" valves.
Not all Presta valves have threaded shafts as shown; some are mostly rubber.
Presta valves come in different lengths. Match the length of the valves that came on your wheels. The deeper your rims are, the longer the valves need to be.
Schrader valves are the same as automobile valves.
Valves usually come with plastic caps. These provide a little protection and a "finished" look. But, many cyclists choose not to ride with them because it's easier to inflate tires when the caps are already removed.