I paid $19.95 for the basic Turbo Tax product. It says I can create up to 4 returns. Am I able to use one of my 4 returns to do my son's tax return?

Yes, you use your four returns for whoever you would like!

How do I create my son's tax return using one of my 4 tax returns?  Note that I have already submitted my tax return, so I have used 1 of the 4 returns for myself, but would like to know how to use one of the remaining 3 for my son's return?

How do I create my son's tax return using one of my 4 tax returns?  Note that I have already submitted my tax return, so I have used 1 of the 4 returns for myself, but would like to know how to use one of the remaining 3 for my son's return?