Student or Learner
Yesterday, I entered a room where some people were talking. I needed to speak to one of them who, when she saw me turned around and stopped listening to the one who was explaining something. The latter, said "oups, sorry" and I said:
"-No go ahead. You can go on, no problem. "
Can you tell me if what I said is correct, please?
not a teacher
That sounds okay to me.
If you feel that your arrival might have created a slightly awkward situation, you could say: "Sorry, I didn't mean to interrupt. Please go on/ahead", or something similar.
We usually spell it "oops".
It's not quite clear who said "Oops, sorry". Was it your friend or the one doing the explaining? In either case, saying "oops" to you doesn't seem appropriate. Perhaps your friend turned back to the explainer and said "Oops, sorry (I didn't mean to be rude to you)".