There are several ways.
You can do it manually by writing it (there are tutorials that cover the subject), use third-party software or use the Super Hatch command found in Express Tools. Depends on how much time, effort and money you want to devote to the subject. However, with all the free hatch patterns floating around the Internet maybe someone has invested all that already and all you have to do is download the pattern and use it.
What kind of hatch pattern are you looking to create?