I'm controlling the sharepoint site for my work group and we have a shared excel doc that everyone uses daily but it doesn't have any privacy ( all information each person adds will be visible to everyone else who uses the doc ). all users have to log into the site individually. is there any way for me to set that document up so that each user can only see what they have added and it all compiles on the back end?
Unfortunately, you can't manage the users' permission on the document content. but, you can manage the permission per document where specific users can see a specific document based on the assigned permission!
If you can divide this Excel file to separate files, you will be able to assign permission for each file for the users who should see the file content!
For more details check User permissions and permission levels in SharePoint
You may also wish to activate Versioning, this will keep track of who has edited the document and build up a history. Go in: Document Settings>Versioning Settings>Document Version History (choose 'Major' or 'Major and Minor' versions).
You can also configure whether or not users can see previous versions of the file from the version history.