Help Concerning Tax IDs and Business License

First off, I'd like to say hello to all of my fellow small business owners, even though that may be a loose term to use for myself, however I'm having a few problems that are confusing me.

Starting July 5th I am going to begin teaching mixed martial arts classes, I already have all of the certification, the space and the gear. Now my only problem is Taxes and business Licensing.

To be honest, I'm not actually running my own business, I'm actually going to teach martial arts in the back room of a friends fitness gym, I will actually be working under him, but I will be in full control of the martial arts classes. I will be getting paid but it is going towards his facility not my own, so I wonder, since it is his business and he is profiting from it, and I am technically only working under him, Would I still have to apply for a Tax Identification Number or would it be somewhat irrelevant?

Thanks for any help.