So what exactly is praxeology?

Is it just the study of human action or does it also include the study of the real consequences of those actions?

I’m asking because I see a lot of times people discussing how from a praxeological perspective policy A or policy B would be acceptable if you would accept a weaker economy as a trade off (i.e. stricter immigration would be acceptable as long as you realize that you will end up with a smaller pool of workers and you think that’s a fair enough trade off for having a more culturally homogenous society).

So is that actually a part of praxeology or is praxeology only the study of human action/preferences?

Praxeology is the study of human action as it is, neither of preferences nor of ends (unless one subsumes ethics under praxeology in the case of the latter.) Preferences are taken to be the ultimate given. What is in the scope of praxeology is of course actions and their consequences.