for the purpose of understanding, the general process is this:
(it will delete all data on your usb stick)
1. download the linux operating system .iso installer file. i386 = 32-bit, amd64 = 64-bit.
2. the .iso installer file has to be put onto the usb stick using a special tool, like unetbootin.
3. switch computer on, press a key to enter the bios and choose boot device, or press a different key to get a one-time boot device selection menu.
4. wait a couple of minutes for the operating system to load from the usb stick. test how it runs and works by using the try mode, letting the desktop load without installing.
5. if everything seems ok, you can find the icon/menu item for installing it.
6. there is a simple installtion wizard to follow if you are merely wanting to erase everything on your hard drive and install a linux operating system over it.
if you only want to delete one drive/partition, then you need to choose the something else option in the wizard. this will require manual partitioning, but its simple once you know how. a default install create:
ext4 mounted at /
swap (1 1/2 times the size of your ram, or just 4 gb should do if you dont want to use hibernate)