This process requires four main steps, namely: 

1. Configuring the Database connection service with your MySQL credentials.
2. Creating Data Models for the different tables you wish to work with.
3. Mapping the tables you wish to expose to your app with the Data Models created in step 2.
4. Using Visual Coding to read from or write to your SQL database (Cloud.DBC.View to list the contents of a table and cloud.DBC.Insert to insert a new item into your table).

Step 1 is described in another knowledgebase article and also in a video tutorial here:

Step 2 can be seen in this set of video tutorials.

Step 3 is described in this article.

and Step 4 can be seen here. 

You will also need to use the backend User Service for the authentication process.
The following set of videos show how to use this service and how to set up a signup / sign-in page.
https://www.youtube.com/watch?v=3Wo0zvU5D4g&t=12s

It is also good to understand the concepts of working with the Aquro Cloud database:
https://www.youtube.com/watch?v=FqSFNwJhy5M
https://www.youtube.com/watch?v=UNznVprlgRw