How to choose and why to choose a certain end are what praxeology attempts to answer comprehensively.
Praxeology is a science because it concerns itself of the outside world.
It makes suggestions on how and why to choose a certain action based on objective phenomena happening in the world. But it does not compel you (it is amoral; amoralism).
What to choose is something that you determine:
- By reason and
- By factors beyond reason
Determining what you want is a task you uniquely are given to answer given the existence of consciousness and free will.