Every file on the site will be added to Assets, such as pictures, PDF-files and text documents. Assets works similarly with the files controlling on a computer.
You need to name the files without any special characters or spaces, so that the files upload properly to Assets. You can separate words e.g. with a dash ''new-file''. Avoid ä- and ö-letters.
When you create a folder or subfolders, you can not change the order afterwards or move files from one folder to another. If you wish to move a file to another folder, you need to upload the file to Assets again.