If anyone else is working on the document, you'll see their presence and the changes they're making. We call this coauthoring, or real-time collaboration. From here, if you'd rather work in your Word app, switch from Editing to Open in Desktop App , near the top of the window. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.