How do I get rom updates?
Updating custom roms is different from getting updates from stock, which involves OTAs (over the air updates) that are done with a press of a button. With custom roms, updates are added online, and it is up to you to pick which one you want and apply them accordingly. Simply speaking, download a rom that is for your phone model, wipe your phone (scroll down here for rom terms), and flash. Do note that if you are s-on (this is an HTC thing, if you want to s-off, check this), then you need to flash boot.img after. To do this, simply reboot into fastboot after flashing a rom, then type in fastboot flash boot boot.img
What happens when I flash a rom?
If you do a full wipe (which is generally good practice), all of your apps and settings will be deleted. This is why it is good to backup your data first. If you looked at the rom terms, you'd also know that dirty flashing will retain data, but may cause problems.