Without screenshots or something we'd just be guessing what the issue is but I'm going to wager the problem is with security. Most likely you're opening the document from an untrusted location and so Office is putting you into "read only" mode. In that mode you cannot do most things other than read the document. HOwever, at least in the Windows version, there is a banner at the top that asks you to confirm that you trust the document and then it enables all the standard features.
Please provide us more information about what you're doing and ideally some screenshots. Also confirm whether this happens with new documents or only existing documents. Finally note that if a document has a macro in it then it is going to be locked down going forward as macros are easy to hack. In newer office versions macro-enabled documents are saved using a different file extension (not sure what that looks like on Mac) so it is clear that the document may run macros.