A window called "Terminal" has appeared on my Mac Pro -what does it do?

I suggest you use the program created by Etresoft, a frequent contributor.  It will provide a snapshot of your system which we can analyze to possibly determine the cause of your problem. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

https://itunes.apple.com/us/app/etrecheck/id1423715984?mt=12

Use the Add Text button to include the Etrecheck report in your reply.

Terminal is like an access port into the engine of your Mac.

Terminal is an Applications, and if you don't want use it right now, just quit the Terminal Application.

Terminal is an apps which allows you communicate with macOS via the command line using Unix commands.

Just quit Terminal. There is no need to delete it.

Etrecheck is worth looking into when you are NOT facing difficulty. I think it has a trial period.