In order to play Free Fire Advance, you need to get an activation code, first. To get this code, you'll need to go to the official website (accessible through the corresponding link) and sign up using a valid email address and telephone number. It's important not to share the activation code with anyone, since each one is unique and personal. It is also important to keep in mind that access to the Advance server is limited, so you may not receive the code for several days.
Free Fire Advance lets you enjoy the same battle royale experience that you're used to, but with tons of new features that will surprise even the most experienced players. That said, all the progress you make in the Advance server won't carry over to the standard version of Free Fire.