Here are 4 easy steps to install Ubuntu on your Dell machine.
First configure your machine to boot from a USB drive, (in most cases that would be pressing F2 or F12 or Delete repeatedly) after the computer starts up until you see the BIOS screen.
Once you boot from the USB drive, you can follow the prompts for installing Ubuntu. In your case I assume you want a clean install of Ubuntu, so choose the option to "Replace Windows 10 with Ubuntu".