In StarBreak, your level serves as a rough indicator of your experience and skill. It is one of the few things that persists through shell death.
Also, your level is used to determine whether you are allowed to manifest as certain shells. In particular, one must be level 3 to manifest as Duskwing, level 5 to manifest as Ironclad, and level 7 to manifest as Fabricator.
Each level requires a certain amount of experience points (also called EXP on this page) to acquire. The first way to acquire experience points and the only one that was available when the game launched on Steam is to lose a shell. At the time of death, your final score is converted into experience points and added to your total experience points, and your new level is determined based on your new total experience points. (If you want to gain levels quickly on death, you may want to look at the Score page.)
In version 1.2, a second way to acquire experience points was added: experience can now be gained while still living by completing missions. Easy/Medium/Hard/Very Hard/Extreme difficulty missions grant 10/20/40/80/160 EXP to living shells upon the boss's death. Brink, being the tutorial mission, does not grant EXP when completed.
Be aware, however, that many missions will only grant EXP to the current shell a certain number of times. In particular:
The elite variants of the listed missions have their own counters:
Graveyard, Temple of the Lost, Elite Graveyard, Elite Temple of the Lost, and Star Cathedral have no limits on how many times they can grant EXP on completion.
Max level serves as the upper limit on your level and also persists through shell death. The only way to increase max level is to complete missions for the first time. All accounts start with an initial max level of 2 and gain 1 max level for the first successful completion of each of the following missions:
Since there are 18 unique missions in StarBreak, the current cap on max level is 20.
Below is a list of the EXP required to reach each level from the previous level (currently a work in progress):