There are two common types of valves that you will find on your bike. The first type is called a Schrader and is what you will find on most cars. These can be inflated with a regular pump or at a gas station.
The second type, called a Presta valve, is thinner and just requires a few easy steps to inflate.
Start off by removing the plastic cap. Next you will have to loosen the nut on the end of the valve by turning counter-clockwise or to the left. You can tell that you have turned it in the correct direction if the nut is at the tip of the valve, and when you press down on it with a finger, air is let out.
Using a Presta adapter, which you can find at a bike shop for $2, thread it on clockwise (or to the right) until it is snug. You can now inflate your tubes with a regular pump to the recommended pressure that can usually be found written on the sidewall of your tire.
Once done, remove the adapter and tighten the nut down so it is snug and at the bottom of its range.
And that’s all there is to it so you can get back to riding.
Previously from Cycle Solutions: How to take the front wheel of a bike