It's like "make things" but for actions. I can't describe it. Also it's "What's the meaning of "to do stuff"" or "What does "to do stuff" mean"

It's an informal and very common way to say you have things to do, in general. However, it would be really helpful if you could provide some context so we can give you a more accurate answer.

就是做东西，没有什么贬义。

Do stuff = do what you have to do. For example: do your homework, or clean the dishes and etc.

"stuff" – things (anything) "Where's all my stuff?" (e.g. my bag, pen, phone) "Shall we get some stuff to eat?" (e.g. eggs, bread, cheese) "You can do more stuff in town." (e.g. go to the cinema, get a haircut, play frisbee)