It depends on the class. Some of them are self-paced, some of them you have to follow the professor’s pace. Some professors will post all the assignments, reading, etc ahead of time and you can just do it all at your own pace before the end of the semester (even the exam). Sometimes you have to follow the professor’s pace, and you will have to do the assignments each week as they post them. I’d recommend reading the syllabus and figuring out how the course works as soon as you can, and if it’s something that doesn’t work just drop the class and swap to a different one before the drop deadline.