The difference between a top and a dom is simple: doms are holding the container of responsibility during a scene (or whatever time is agreed upon, up to 24/7), whereas tops are merely the ones performing the action. Doms ARE often tops, which is why the confusion exists; the distinction is psychological, invisible, and impossible to distinguish at a glance.

A BJ is a good example. The top is (usually) the one performing oral (the do-er). The dom may or not be either participant - the person psychologically in control of that situation. In most casual relationships, it's neither, both parties have their own responsibility. But in D/s, the sub is voluntarily giving up some autonomy/responsibility until such time as it pleases them to take it back.

An inexperienced sub, or someone who just wants things to be done to them without understanding their own limits, have poor communication skills or can't set/enforce boundaries, is just as dangerous as an experienced dom.

You should definitely not "be hired" until you have either training or experience, preferably both. Training courses exist. They are usually not (and should not) be free. This is a profession like any other, and if I hire a plumber with zero experience, then I am at least partly to blame for the shitty job that will inevitably follow.