OneDrive is a great place to store all of your documents.
You can create basic Word, PowerPoint, Excel and other Microsoft programs directly in OneDrive, but can store any kind of file (pictures (jpg), videos (m4s), PDFs, etc.).
Collaborating on and sharing documents with others through OneDrive is also a great feature. Note some teachers may not want you to "Share" documents in this way as there is currently not a good way to sort and control documents.
All students should follow good organizational habits: creating folders for each class and saving documents (with clear and distinct names) in those folders for easy retrieval.