Occultism (if you strip away the theological conundrums left over from a time when no one knew better) is, at it's very core, brain hacking.

You exploit weird glitches in the brain/body to access a plethora of abilities and differing states of consciousness that we aren't supposed to be able to access.

There are dozens of traditions that have their own techniques to accomplish these feats as well as explanations as to why it all works.

To become an occultist all one has to do is study a subject of occultism that strikes your curiosity the most and branch out as you see fit.

While you could just join a group or lodge that will teach you I would highly recommend you study alone first and get a feel for your interests and what you're skilled at.

Hope that was helpful. :3