Hey, Savio, those guys in the picture are down on their left knees. When you genuflect in church, you go down on your right knee if you are able. Able, as in, not injured or something.
When I say chapel, I mean a separate room within the church. I attend Mass at a Cathedral, which has the main church (can be called the nave) and several small chapels off to the sides. Each chapel in my Cathedral is like a small church, with an altar, tabernacle, pews, etc.
Some churches have their one and only tabernacle in a small adoration chapel away from the hustle and bustle of the main church. People can go there to pray in peace and quiet. If that’s the only place where the Holy Eucharist (or Blessed Sacrament) is reserved, it’s nice to stop in for a personal moment with Jesus every time you are in your church. Just a minute to say hello, I love you, or whatever.
If your tabernacle is in the main church, you can have your personal moments with Jesus right there. Again, it’s a manners thing. When you visit someone’s house, you certainly want to see them in person and thank them for inviting you, and say hello and goodbye.
The word “sanctuary” is used for the area right around the altar, where the action of the Mass occurs. In older churches, it’s the area behind the altar rail. In newer churches, it’s often a step or three above the main floor. In protestant churches, doesn’t it mean the main church?
Betsy