The literal meaning of get up is to rise or ascend, physically. When someone gets up, you also mean that the person awakens and gets out of bed and if you wake them, you can say, you get them up.
Ex: John! Can't you hear the phone ringing? Get up from the sofa and answer it! It might be your grandma to talk about grandpa's birthday party.
Ex: I always get up by six-thirty on weekdays so that I have time to get ready for work. I want to impress the boss by always being on time!
Ex: Do me a favour and get me up by eight o'clock, okay? I don't want to be late on my first day of university.
When something starts to happen, for example, a storm or the wind, it gets up. It can also be used as a synonym of gathering the courage to do something.
Ex: The wind got up over the course of the afternoon, until by dinner time, it was a gale. It was so powerful, it knocked me over. I could barely tolerate it!
You can say that you are getting something up if you are trying to organize a group of people for an activity. But if you say get up to something, it means that you are doing something, probably something that someone else wouldn't want you to do.
Ex: I was able to quickly get up nine more people for a game of basketball. We really had a good time playing.
Ex: The cat is making so much noise in the kitchen, I know she must be getting up to something in there.