If you do not know how to do that very simple thing, then how can you start the business?
How can you even think of starting a business that you have no experience in?
The first thing you need to do is go to a trad show where they have t shirt making equipment, find the equipment that you want to use, and then find out where you can train on it.
If you do not know how to use your equipment, you will make so many mistakes that people will not come to you and you will go out of business.
AFTER you have trained on the machines, then you need to find a CPA and pay that person to sit down with you to make a business plan.
If you do not have a business plan, no bank will lend you money to start your business. No one anywhere will give you a business loan without a business plan.