Beck from blanka here. A helpful article for your question could be one that I’ve written recently, you can find it here. The link will bring you to the exact spot you can read about the type of designs you can do for your t-shirts/apparel (great store by the way!).
In a nutshell, consider the 3, most common types of logos: Wordmark logos, Monogram logos, and Combination logos. These three will allow you to have logo variations for your apparel.
Hope this helps!