I recently attended another parish and this Sunday I wish to go to Confession there. However I don’t know when to enter the confessional. There is a red light above the door of the Confessional, so should I enter when this light is on or off? Also should I knock on the door before I enter?
Ahhh - the confessional - where one red light means GO, and two mean STOP. At least that’s how it is at our parish. When we first started attending confession on Saturday afternoons, rather than at the once or twice a year penance service (where there is always a line), the lights were a big hurdle. The first time, I just sat there and watched for a while. Then I sent my younger son ahead of me to scope it out.

(Might have knocked that time, but in general, there is no need to)
We have an “old-time” confessional that has apparently been modified to have a face-to-face side. The priest sits in the middle, and if the red light in the middle is on, that means he’s there. If there is another red light on, that means someone else is there, too.
I always go to the face-to-face side (the wall goes about half way up, and there is no indication from the outside which side is which), and twice Father has put his hand up in mid-confession to stop me, as he heard someone enter the other side. He leans over and tells them through the screen that he can only hear one at a time, and waits until he hears them exit. Then we pick up where we left off. His ears are better than mine, because I never heard a thing. This happened twice in a row. The next time I went, I told him that if someone walked in, I was going to buy a lottery ticket when I was done!