to add new generic node, go to toolbox tab, add generic node subtab, then:

1. specify where to insert the new datablock node by clicking on one of grey bars on left panel
2. enter the header text of new datablock. Use 'verify and render' to verify entered text and to see the preview of new datablock header display
3. if datablock has a unit, click 'browse' link to select from available units.
4. once unit is selected, you may click on it to remove it