Many that start their training in jiu-jitsu always feel a bit overwhelmed with all the new moves they are learning. Also many new to the sport find to have some kind of anxiety of going to their class and rolling. These are all concerns for new students in jiu-jitsu.
There is alot to learn when you first start out taking jiu-jitsu. When I started, it was all no gi classes and I would get killed on the mat on a daily basis. I ended up stopping my jiu-jitsu training. A couple of years later I went back to training in jiu-jitsu but with the gi only and I love it.
When I started training again I would simplify the move. When practicing on the mat you should do the same thing. If they teach you an armbar from the mount break the move up into parts as you train it. Now you won't master the move your first night or even after taking a hundred classes. Step by step take each part of the move as you do it and focus on making sure that your positioning is right and that you are following the steps as closely as your teacher was when he or she was teaching the move. This will help you out in the long run as when you begin to roll live these movements will be embedded in your brain and you will be able to control you and your opponents movements.