Newbie question : level and damage

Hi all,

Here are some other newbie question:

1. What is the use of the level? Right now, I am level 52. I have 4000 stamina points, so if I start a mission, I quit, I start, I quit... several time, I guess I can rise up to 60 may be 70. Any interest ?
2. How are calculate the damage ? My gardian bullet does 702, my focus lazer 4917. What is the formula?

Thanks a lot