Can someone explain what birth control pills will do for my cycle?

I started taking the pill a couple of weeks ago for the hormone regulation and I’m realizing I don’t know much about it. I have always had irregular periods, so I wanted to give the pill a try to see what would happen.

So my cycles are usually around 38 days long, but occasionally I skip one altogether. I’d like to know anything from how the pill works to what it does to menstrual cycles. Will I be on a 28-day cycle now? Why/how can you have periods if the pill prevents eggs from dropping? Am I feeling really emotional as a side effect, or is that psychosomatic? :P