What do you normally say when praying at the pagoda in Pchum season?

I've been visiting the pagoda with my family during Pchum season and I'm not sure what to say when I'm praying or lighting incense sticks. I've heard people suggest saying certain phrases, but I'm not sure what they mean or how to use them. I'm trying not to feel wasteful, but I also don't want to make a mistake.