When Catholics enter a Catholic church and before they sit in a pew, they genuflect down on one knee. This is done for 3 reasons.
1. The getting down on one knee is a way to be humble before Jesus. This is an open gesture to show recognition to the presence of Jesus in the Tabernacle that holds the Eucharist, usually placed behind the altar. * While down on the knee, the sign of the cross with the right hand is done.
2. We genuflect to adore Jesus to express that He alone is Kings of kings and Lord of lords.
Philippians 2 :9 Wherefore God also hath highly exalted him, and given him a name which is above every name:That at the name of Jesus every knee should bow, of things in heaven, and things in earth, and things under the earth;And that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.
3. Genuflecting is also another way we say to Jesus we love him and want to love Him for the rest of our lives. This is similar to the way a man would propose to the woman he loves and get on one knee in asking her to marry him; he is saying he loves her and will for the rest of his life.
*In some modern Catholic Churches the Tabernacle is not build behind the altar. In this case, before entering the pew a bow is appropriate instead of the genuflect on one knee.