Downloading:There are two basic ways to download linux. You can download it normally though your browser or you can torrent it. I prefer torrenting my distributions as it is faster. Just download a program like utorrent and go to the download page of your specific distro. Linux distributions are downloaded in the format .iso. This is what is called a disk image and it must be burned onto a cd/dvd or specially formatted usb in order for it to be loaded onto the computer.
Burning:If you are using windows you can use a simple program like
this to burn your ISO to the disk. Using the program in the link provided you simply open the file you want to use, select the cd/dvd drive you want to use and make sure there is a blank disk in there then press burn. You can name the disk if you want but it isnt exactly necessary.
usb install:If you want to use a USB port to test out linux then do the following. Go to
this site and download the Universal USB installer program. This is the program that installs linux onto the usb stick. It is very straight forward. Simply select the distribution you will be using. Then select the .iso file on your computer. Finally select the USB port you want to use and weather you want the program to format the usb stick before hand. Then click create.
booting:Booting from a disk or usb is the same process. What you have to do is access your computers BIOS screen. BIOS stands for Basic Input Output System and it is the system your computer runs before windows or your alternative boots. Ususally this can be accessed by pressing f11 when you turn on your computer. I have had the bios access button be f2 and f12 as well so it is a good idea to google the exact button for your computer. When you are at the BIOS screen tab over to boot options and make boot from cd or usb the primary boot method. Save and exit.