You can use the Files page to upload or manage documents accessed via the Settings menu on the left-hand side menu:
Attachments can also be uploaded and added directly to an entry via the Information tab:
Select the Upload files from the Files page to select a file to upload. Documents are restricted to 15Mb per upload, enough to handle most file types.
If you want to edit the title of a file, select the pencil and paper 📝 icon and type your changes.
To delete a file, select the bin 🗑 icon next to the file name, then OK when the below message pops up: