Acts 2:36b (KJV) says,

God hath made the same Jesus, whom ye have crucified, both Lord and Christ.

The word Lord is kurios in the original Greek, and it means having power and authority; controller, lord, master, owner.  Kurios is the New Testament representation of the Hebrew word that is translated Jehovah or Lord in many Bible versions.  When Jesus died for us, He bought us back from the kingdom of Satan with His very own blood, so we are not our own.  When we are born again, we accept Jesus as our savior, but we should also honor Him as our Lord.

Jesus is Lord, and as we believe in our hearts and confess it with our mouths, we choose to make Him the Lord over our hearts and lives. (Romans 10:9-10)  As we declare His lordship over us daily, we enthrone Him as Lord over our thoughts, words, decisions, behavior, relationships, finances, actions, gifts- every aspect of our lives.  This allows Christ to rule in and through us, where He causes us to win, triumph, and overcome.  We enforce the lordship of Jesus in an area in which we may be struggling by confessing that He is Lord over that area. 

Acknowledging Jesus' lordship means we do what He wants us to do: give, pray, read the Word, obey His teachings, etc. In this way, we bring ourselves under His rule and control.  This requires that we humble ourselves and allow him to take the lead in our lives.  Too many people don't want to release control and they end up doing life their own way.  That brings about results that are less than ideal, sometimes even disastrous.  Such people have made Jesus their Savior, but not their Lord.  And then they demand to know why "God allowed" their situation to turn out poorly!

If we will humble ourselves, consistently confess that Jesus is Lord, and stay in His Word, we will see the lordship of Jesus reflected in our actions and reactions.  For example, when we are treated unkindly or unfairly and we choose to love instead of seek revenge, we are bowing to the lordship of Jesus in our lives.  That put us in position to be victorious.  And who doesn't want that?