Im not a pro but I've been doing it for fun for many years. First, be ready to spend a ridiculously long amount of time reading, watching videos and if you get the chance, talking with and watching a professional. There's a ridiculous amount of things to learn and every technique requires weeks, months and even years of practice just to get decent at them. Also keep in mind that not everyone is good at everything. Its possible and normal that you'll never perfect certain techniques and some you could even be terrible at. Also be aware of what you can or can't do before tattooing anyone! Tatts are permanent and not always easy to fix.
All that beng said, its a hell of a lot of fun and very satisfying when you finally get to see your art on a satisfied client.
My best advice to get started is to start by learning everything there is to know about the equipment you have. Lear how to change parts,repair it, modify it, protect it, clean it, sterilize it, etc. Followed by how to set it and use it. Then, I recommend actually using it a bit to know how it handle and have a better understanding of further instructions on technique. You can buy fake skin for practice from any tattoo supply shops or if you want the real feel, nothing beats pig skin. Most butchers should have it/be able to get it. When that's done, start with the basics like sanitation, proper handling of equipment, how to set up, etc., followed by basic techniques like outlines and solid colours. i recommend practicing them for a while before moving on to make sure you don't accidentally mix up info or forget things. Once you're comfortable with the basics, you can move on to more advanced stuff.
Keep in mind that this was a very quick overview and there's tons of other stuff to know but this should get you in the right direction. You can also pm me if you want advice on products or sources for info as well or any other tattoo stuff really.
Have fun!