You need to click on the torsion-general button, then click 4 atoms that describe the torsion - the first atom will be the base (non moving) part of the atom tree, on clicking the 4th atom a dialog will pop up with a "Reverse" button. Move this dialog out of the way and then left mouse click and drag in the main window will rotate the "top" part of the residue round the clicked atoms 2 and 3. When you are happy, click "Accept".
If you are torsion generaling a residue that has an alt conf, then the atoms of residue that are moved are those that have the same alt conf as the 4th clicked atom (or have an blank alt conf).
For ligands, you will need to read the mmCIF file that contains a description of the ligand's geometry (see Section Regularization and Real Space Refinement). By default, torsions that move hydrogens are not included. Only 9 torsion angles are available from the keyboard torsion angle selection.