H. RES. 1621 establishes that it is the policy of the United States to allow Ukraine to use U.S.-supplied long-range missiles against military targets within the Russian Federation. This resolution responds to the ongoing conflict following Russia's second invasion of Ukraine...
Simple Explanation
The U.S. government wants to officially say that it's okay for Ukraine to use weapons from the U.S. to protect themselves, even if that means using them against Russian military places. This idea is because Russia has been causing problems in Ukraine, and the U.S. wants to help Ukraine stay safe.