Yeah, so that’s due to Google Sheets wanting to tell you that someone else is also in the same sheet. It assigns each person a moniker as “Anonymous (animal)” and shows you what cell they are editing (often times they are idling).
Due to this (and the collaborative nature of Google Sheets), someone may edit a cell while you also are trying to - however unlikely since I doubt dozens of people are going to try to use it simultaneously.
What I recommend is you go to the upper left menu and click “File” and then “Make a Copy” to copy it to your own Google Drive so it isn’t shared with lots of people. Also, I have an Excel spreadsheet I can share that is identical, Google Sheets are just easier to share and are free.