Now that you know how to enrol, you might be scared of how many subjects there are to complete and don't know where to start. I have a few suggestions. These are just my opinions you are free to have your own. 

I would suggest starting with Charms. The first couple of lessons show the basics of spell casting, some facts about wands and some very handy charms. The assignments are not to difficult and it introduces you to note taking which I would suggest for all classes. Professor Laurel is very kind and understanding and will help you out with any charms problem's. The PA's for charms are very fast and knowledgeable so your assignments will be graded fast without cue's. The lessons are also quite short and the language used is easy to understand. 
Some spells you learn in charms are the Severing charm, the fire-making charm and the rocket charm.