Create the tee shirt designs as a generic logo

Hello all, I need some help with this.

If I make my focus 'Sell my own designs', can I create the tee shirt designs as a generic logo (like...Your Team / Baseball) and have the customer change the text? Adding text in place of 'Your Team'?..

It seems like that is something that should be happening, but when I open it all in a new page, it doesn't let me edit the design?

How do I do this? Someone please help...