If you open up the data connections.
Select the Main data connection for your form.
In the lower window it will show the details and it will say recieve only or submit and recieve.
If it says submit then you are all set and you just need to add a submit button or trigger it somehow and the data will get saved back to your table.
One thing to remember with the basic form is that it is not very smart and will write all data back into your table. So if you are manipulating data in your form which is in the data fields then it will update your table with this which you may not want.
If submit is not listed as an option then your table is not setup correctly with a primary key. You should be able to set the Primary key and then modify the data connection and go through the steps again without starting over.