How do I go about using my son's license code? He only used it once.

Your son's desktop software can be used on computers that HE owns.    You can use the desktop software to prepare and e-file up to five federal returns (and the state returns that go with them for a $25 state e-file fee).   If you have access to your son's computer, launch the 2024 desktop software and go up to the tool bar at the top of the screen.  Click FILE and then the drop down "New Tax Return" to start a return for yourself.

Make sure you are really using the desktop software and are not using online by mistake.

We see people get confused and they keep logging in to online software which will require them to pay at the end.   You need to use the desktop software.   One way to tell if you are using the right software---your tool bar.   Online software has the toolbar in a black vertical column on the left side of the screen.   Desktop software has the tools up on the top of your TT screen.