If these were your personal computers that you sold for a few dollars as a one time thing, you really do not have to do anything. Your transaction would be similar to an on-line garage sale. See the following link for more information:
If you sold the computer as part of a business you started and planned to continue, you should report that business as such. The following links will help you with that. The most common type of first time business is reported on IRS Schedule C.