How do I reboot my PC?

Simply turn it OFF and ON again.
Otherwise we need more information to clarify your question.

When a PC is started from the powered down state, you get what is called a cold boot. If your at the desktop with the PC on and you select to turn off the PC but select restart instead, that is a reboot (it's already booted and you want to do it again). Many programs you install request you to reboot the PC after the install finishes so they can initiate certain functions (not all of them desirable). I don't like to have too many apps start with Windows, I prefer to start them only when needed, but a lot of apps will not install properly unless you allow this and reboot. Then it's up to you to go into their settings and tell it not to start with Windows after its installed.