TSA Pre-Check is a valuable service for individuals who are frequently flying domestically, making the airport security check in process faster and easier.
You can learn more and signup at the TSA's PreCheck website.
Global Entry, on the other hand, makes entry back into the USA after international travel faster and easier. We recommend this service to individuals who frequently fly internationally. If you apply for and receive Global entry status, you automatically receive the TSA-Precheck status.
You can learn more and signup at the Customs and Border Protection website.