Your character in Elex is fundamentally built by the five different attributes you can control each level you gain in the game. Each level will give you 10 points that you are able to distribute between them and also 1 ability point which you can spend on abilities.
There are five different attributes you can raise each time you level which will give you more damage, more health etc depending on the one you select). They will also determine what armour and weapons you can use depending on the number of points in each. These are the following five you can select.
The other part of developing your character is the abilities you learn from different trainers around the world. For this, though you need to find the correct type of trainer, have the right amount of attribute points in each area and then buy the privilege to have them teach it to you.
Of the base abilities, there are also the specific faction skill trees, Berserker, Outlaw and Cleric. Here are the full list: