When entering the Catholic church what are you doing when you kneel before mass begins?

The genuflecting in the aisle or kneeling before you enter the pew is actually how we salute the blessed sacrament (the real presence of Jesus) in the tabernacle. On Good Friday, you may notice that some people do not do this because on this day the tabernacle is empty in mourning of Jesus' death so his presence is not there.

**EDIT** I just reread your question and I think now that you are not talking about the genuflection before entering the pew, but rather the kneeling in the pew. If this is so, it is just a time for private prayer, there is no specific prayer that is said. People just take a few moments to reflect in prayer in the presence of the Lord before the larger communal prayer (the mass) begins. You may notice that some stay behind afterwards to do the same thing.

If you're talking about the bowing or genuflecting that a Catholic does before entering the pew, that is to show respect that you're entering God's House. Otherwise, most Catholics, once they've entered their pew, will kneel and pray before the service begins.

Worshipping an idol = idolatry.

My 2 cents.

Psalms 115:4-8

Catholics genuflect when entering and leaving a Church (or a pew).

Kneeling on one knee is a sign of honor and worship to Jesus Christ and an expression of faith in his real presence in the tabernacle as consecrated bread.

Making the Sign of the Cross while genuflecting is optional.

With love in Christ.