Write out all the information you want to include on the t-shirt. This should provide a good overview of the event, without overdoing it. For example, if you're making T-shirts for your son or daughter's college graduation, you'll want to include their name, the school, the year, and possibly the location.
Find a t-shirt that has a design you like. This could be something from a store, your closet, or even one you see on a billboard. The only requirement is that the shirt should have a good amount of text on it.
Create a design mimicking that of the shirt you like, but using the graduation information. Use Microsoft Word to make the design, (go to View, Toolbars, Wordart for more creative text-design options).
Find a t-shirt design website or local print shop that suits your needs. There are many that are easy to find online and their prices and services vary, so shop around.
Double-check that all information is correct and properly spelled.
Upload the design or finalize with the print shop, and order your t-shirts.