In Brick-Force, when you play you will gain experience (XP) points. Under your character you will see an experience bar what tells you how much you have done of your current level (0-100%). You will get a level when you have enough XP points and your bar reaches 100%.
When you first start playing Brick-Force you are on Level 1 and known as "Trainee". It's very easy to level up the first few levels but it gets harder later on.