If you are creating a database type form. You created it initially linked to a database then it will have some basic limitations that you will need to work around.
One of those limitations is the table must have a proper primary key and foreign key realtionships with any child tables or you will not be able to submit to it.
If you look at your main data connection it will list whether it can receive only or both receive and submit.
Once this is able to accept a submit just create a button and give it a rule and action to ssubmit the main data connection and it will push the information back to SQL.
If you want to have really unlimited interaction with your SQL data, query more than one table dynamically, submit to more than one table, then you need to use web services.
You can email me and I could show you how they can be setup and used.