For more details have a look at the official documentation at http://edocs.bea.com/wls/docs103/secmanage/rdbms.html
Oracle recommends that you configure your RDBMS security store during domain creation using the configuration wizzard.
This is by far the most easiest way to do the job. The only thing you have to do is to start the wizzard. Select "Create new Weblogic Domain", tell it the prefered user name, template and JDK and here comes the magic:
Tell the wizzard, that you would like to "Customize Environment and Service Settings". The first page, that displays after this is the "Configure RDBMS Security Store Database".
Fill in the required parameters and click through the remaining pages. Finish the wizzard but DO NOT start the server.
Now you have to create the DB tables. Look at the
Thats all for now. Now, you are ready to use your new RDBMS based security with WLS and MySQL.