The Speaker of the House of Representatives is responsible for assigning bills to a House committee. This is one of the early steps for a bill to become a law.
There are many committees in the U.S. House of Representatives that can hear bills. For instance, a bill that addresses an issue pertaining to domestic security would be referred to the Homeland Security Committee. A bill that is meant to address highways would be sent to the House Transportation and Infrastructure Committee. Because the Speaker gets to make these decisions, whomever holds this position enjoys significant power in the legislative process.