Upper Intermediate - ‘了’‘到’‘过’-what are the differences？

Hey, I was wondering if anyone could tell me what the difference is between verb+了/到/过/到过/到了。。etc

Even though I have been studying chinese for a few years now, I am still abit fuzzy on this. I understand the basic verb+le (verb completed pattern). Is dao/guo just a different way of saying a completed verb?