Common File Locations for both Mac and Windows Users

...

To see the size of a specific file or folder, click it once and then press Command-I. To see storage information about your Mac, click the Apple menu in the top-left of your screen. Choose About This Mac and click the Storage tab. For Time Machine backups, it's good to use a drive that has at least twice the storage capacity of your Mac.

Windows: Right-click on the desired file or folder and select "Properties". The amount of information will be displayed under "Size".

macOS: To see the size of a specific file or folder, click it once and then press Command-I. To see storage information about your Mac, click the Apple menu in the top-left of your screen. Choose About This Mac and click the Storage tab. For Time Machine backups, it's good to use a drive that has at least twice the storage capacity of your Mac.

...

General user data is anything that you have put on the computer, including desktop icons, pictures, downloads, documents, music, movies, etc. This is commonly referred to as personal data.   If you backup the file locations below, you will backup your personal data.  Note that university-owned computers generally redirect user data to central servers rather than load it on individual computers).

Windows: Open "Computer". Double click on your File Explorer" (folder icon on the task bar). Click "This PC" on the left, double click on the C: Drive. Here there will be folder entitled "Users". You can save all the users as a whole. Or, open this folder to find each individual user on the computer.

...

macOS:  Documents can be found in Finder > Go > Documents. These can then be dragged and dropped onto the back up device of your choice. 

Note: These are the default save locations for  documents, but that doesn't mean they will always be there if you have changed that location. Keep in mind where you are saving your files so you can recall back to them when necessary.

iTunes Library

Windows: Follow the General User Data instructions above. Under the desired user folder, click on "Music." There should be a folder entitled "Itunes Library".

...

Windows and macOS: Microsoft has instructions on how to backup your Outlook contacts: Outlook Contacts Backup

...

...