Once you have applied the merchandise template you want to use into Procreate.
You will have complete freedom to compose it however you want, to explore design ideas.
Add colors by dropping them into the desired sections and add textures where you feel needed.
Once you apply the color, you can adjust the opacity and the blend of each section to get it just right.
From there, you can add your logos and designs on separate layers.
This is where the magic happens. Customize your merchandise template how ever you desire!