Find someone that specializes in graphic design or photography to get the right image that you want on the shirt. Once you get the image take it to a printing shop and see if they can print that image on the shirt. It may cost you like $15

Silk screen owners can make them for you but it will cost for the shirts and the printing. You can print on fabric but silk screen is more popular and the printer toner is very expensive. A profit would depend on your cost of product, shipping and handling and sales price and if you can sell all you have made in the correct sizes. Also you may find you want to wear one so you have one less to sell.

I have a semi famous instagram account (5,000 followers) and i want to make a t-shirt for it having my cat on it to sell to others. How do i do? Will it cost money? And will i make a profit?