Determine the type of valve you have. Bicycle tires almost always come with Presta or Schrader valves. Schrader is the more traditional of the two and are wider black plastic valves with a cap; they are just like the valve on your car tires. Presta valves are small skinny metal valves with a little screw nozzle at the top. A third type of valve, Woods/Dunlop, is very rare and can be inflated with a Presta pump attachment.
Unscrew the valve. For a Schrader valve, unscrew the cap and take it off. For a Presta valve, unscrew the cap and then open the nozzle by unscrewing counter clockwise.
Make sure that you have the right pump for the type of valve that your bike tire uses. If it is a multi-valve pump, be sure you are using the correct attachment or setting.
Secure the pump to the valve. If there is a locking lever, be sure to lock it, which is usually done by pulling it up. If there is no locking lever, hold the pump head firmly to the valve.
Pump up your tire by pressing up and down on the bike pump.
Use the gauge to check the pressure based on your tire requirements. If you don't have a gauge, squeeze the tire to make sure it's filled enough.
Open the pump lever and pull the pump off the valve.
Screw the nozzle and/or cap closed, and you're ready to bike.