I need help figuring out how to add a column to a list of zones. When I open up the attribute table, I'm unable to click the edit pencil because it's grayed out.

Ultimately, I'm trying to transfer data in a column I have in excel into this zoning shape file.

I tried searching for a solution to this issue - since it's seems pretty basic - but wasn't able to find anything, so apologies for the noobie question.