Here is a complete guide to creating customized repeating patterns in GIMP and then adding and using them from the Patterns library.

The easiest way to spruce up text in GIMP is using the "Alpha to Logo" filters which are a pre-made selection of effects.

How to Make Text Appear to Be on Clothes in GIMP. You can add a text layer to a picture to make it appear the text is written on an article of clothing like a t-shirt or jacket.