@ Rebecca
You would only ever receive that error is Connections was not uninstalled correctly by WordPress which happens on rare occasion during updates a WordPress fault, not Connections.
To fix, log into your site with FTP and navigate to the ../wp-content/plugins/
folder and then delete the connections
folder.
Now you will be able to reinstall Connections normally.
If you already had data in Connections, it is safe in the database and will not be lost.
As for installing extensions and templates, that is done exactly like installing any other plugin which needs to be uploaded. Here’s the link the doc page which has the basic installation instructions for extension. Template are the eact same process, here’s the basic installation instruyctions.
Specific instructions for each extension and template can be found on the docs table of content page.
Hope that helps! Let me know.