Theresa,you will have to create a Thing using the MySQLServer ThingTemplate ( which got imported when you imported the extension) and configure it to connect to your MySQL. Here's the outline with some screenshots for you to get started:
1.Since you have already imported the Extension, create a new Thing with MySQL Server Template like so and Save the thing:
2: Navigate to the Configuration section of that newly created Thing and provide the connection string, username/password to connect to the DB
3. Once configured, make sure to save the Thing and then you can validate the connectivity via the isConnected value in the Properties section
4. Afterwards, you can create the SQL Services from the Services section of thing
You can also refer to this blog post How to configure Oracle 12c's Pluggable Database as External DataStorage for ThingWorx , for reference, even though its for Oracle but you can get the idea how services are configured in the Services section.
Hope this would. Let us know if you are having issues in connectivity.