when u reached rank 11 u can chose your u get your first carrer pont that u can use to start a carrer with lvl 40 u have than 25 points and u can bring one carrer to the max.
If u dont liek your build u can reset it how often u want for a few silver or Gold
look here these link will help u
just choose your class and then look what effect wich carrear tree is the best 4 u and if u don't like it just respace it later
press thx if i helped