Printing to the Zebra branded thermal transfer printers requires knowledge of their proprietary EPL2 language. Searching the net for a nice way of using EPL2 to communicate with these printers turns up a number of small projects, though none of them particularly ideal for integrating with a well written C# application, with most of them effectively getting you to copy and paste code into your project that you shouldn’t have to maintain.
Sharpzebra is a new open source project, written in C# that gives you access to a better printing API that abstracts away the EPL2 language concepts. I hope that it helps you spend more time putting together the things you need to print instead of working out how to print. See the Two Minute Quickstart here.
Download the binary release (dll), or binary with the project source code here.