Ahnne,
Your questions seem to indicate you don't understand computer terms. Rebooting a computer means simply to close down all programs and cycle the power on the computer safely. You will be given the opportunity to save documents on programs being told by the operating system to quit. If you don't allow a program to quit, the reboot sequence will be interrupted and the computer will tell you its reboot sequence was interrupted by a certain program. To reboot the computer, go to the Apple menu (has an Apple logo on the upper left corner of the screen), and select Restart.
The only time files get deleted are if you empty the trash after putting them in the trash. The trash is on the bottom right corner of the translucent bar on your screen known as the "Dock" as long as the Dock is on the right or bottom side of the screen. It is on the bottom left if the Dock is on the left side of the screen.
If you choose to erase and install your operating system, that's the other time files get deleted, or if there is damage to the file system.
The word delete means to erase, and wipe out entirely from existence.
I suggest getting a computer dictionary or looking for one online in Google, as your lack of knowledge may be dangerous to your usage of your computer. Don't use it until you get better knowledge of what certain terms mean.