1. Go from "Downloads" to "List of Releases" and download the ISO of your favorite flavor from "Download Package list". There are screen samples of the desktop and start menu in "Image Gallery" so you can refer to them.
2. Burn downloaded ISO to USB or DVD. DD mode is recommended.
3. Insert the installation drive into your computer.
4. At startup, open the boot menu and select to boot from the installation drive. Don't forget to disable Secure Boot.
5. Depending on the flavour, if you wait for a while, the login screen will appear, so select "Log In". You don't have to enter a password.
6. When the desktop is displayed, select "System Tools" → "Install System" from the start menu at the lower left.
7. Follow the on-screen instructions for installation.
8. Reboot when done. After rebooting, unmount the drive (it might break if you forget this) and remove it from your computer.