If you find it easier to select people based on relationship, select File menu > Export Partial > Select Enter the names of people and then select their descendants, ancestors, or whatever by changing the Relationship Filter. Each time you click the Select button you will add the individuals selected. If you make an error, just click Deselect to undo the latest selections or Clear to remove all selections.
Proceed to create a gedcom file containing the people you selected. (the ones marked with the >> symbol)