There are a few methods used in these modern times for graphic tshirt printing and each has its own advantages and disadvantages depending. When you know what the printing methods are and what the different reasons are for choosing them you can then better choose what best suits you.
Heat transfer printing
This is a type of printing method that does exactly what it says, using heat to transfer an image from heat transfer paper to the cotton tshirt printing or what else you might be printing on. The chosen image is printed onto the special paper and then when heat is applied it bonds to the material of the garment. Printers use a heat press for industrial-sized printing needs, but the same principle works for people doing it at home with their irons on a much smaller scale. This method allows you get to have images and even more complex photographs printed without a lot of setup or mess required.
But there are some limits to this printing method including for every shirt you want printed you have to go through the whole process of cutting the shape on the paper and taking out anything that you do not want on it the shirt. If you want more than a couple of shirts it is a process that takes some time. It is not something you can do bulk orders with.
Digital printing
Digital printing is a more recently developed printing method and is suitable for graphic tshirt printing and growing in popularity. It works much as a regular printer does but the printer is larger and it prints on the garment. There is no having to set up or go through a process for each tshirt so you can use the same design on a large number of shirts, easily and quickly. Digital printing is great for when you have images that have many colours, photographs you want to reproduce on shirts and so on.
The only thing to consider with this method is that it costs more because of the time it takes to print in large quantities. It is also a factor that with some of the older options the prints fade away sooner than most people prefer, especially considering the cost. But there have been developments made to work on that and things are changing and improving all the time.
Screen printing
Screen printing has been around for hundreds of years and remains one of the most popular options even now. The final result looks great, colours are bright and they last a good amount of time. When you order in bulk you get it a lot cheaper than other printing methods too. The only thing about doing cotton tshirt printing with screen printing methods is that the more colours used, the more screens needed, and if there are going to be orders of the same thing again the printer has to store the screens. It is also not the best option for photographic images.