Your question is much too broad to be answerable here, but my first suggestion is to find a specific task that you would like to try to implement. The first time I used PHP and an SQL database (PostgreSQL for me), I was building an address directory to attach to a web site I had previously written for my college reunion class. Having a specific project helped to focus my mind on what was involved.
However I strongly recommend you dump phpmyadmin and start teaching yourself how to write SQL using the mysql or psql command-line clients. If you want to understand how to write SQL-based applications, you need to learn SQL and not have some graphical client generate the code for you. I'd start by creating a small database in a spreadsheet program, then saving the data and loading it into an SQL database. Then teach yourself how to run SELECT queries with WHERE clauses like this:
Then try some INSERT and UPDATE commands. After that you can write a couple of simple PHP scripts to run those queries and display the results.
select * from myfriends where lastname='Jones' and firstname='Shirley';
Expect to spend at least a few person-weeks on just simple tasks like these if you have no experience with SQL or programming. If you've written programs in a procedural language like Python or perl before, you'll find the PHP part less daunting than the SQL part. If you're starting from scratch, I suggest using PostgreSQL rather than MySQL. Postgres conforms more closely to the SQL standards than MySQL, so what you learn will be more transferable to other SQL databases like Oracle or MS-SQL. I once had to write an application that queried an Oracle DB and found the syntax pretty similar to what I was used to from using Postgres.