Once your understand the basic etiquette of the mats and how the structure of a typical Brazilian Jiu Jitsu class. The most important action you must understand before stepping onto the mats is how to tap out.
Maybe you watched UFC fights before and you see 1 fighter beat another by making the losing fighter “tap” their opponent with their open hand 2-3 times of more. The tap is very important in MMA and in BJJ as signifies the fight is over and 1 person has called a stop to the fight or training.
In fact respecting the tap is rather not respecting the tap is one of the biggest cardinal sins in fighting. Professional Fighters have been kicked out of promotions and BJJ student have been kicked out of gyms for not respecting the tap.
For a new student tapping early and often will keep you safe on the mats and will keep injury free in the long run.
Here are a couple of videos explaining how to tap out: