For a custom race, you would need to go to Actor Data -->Race in the geck, Double-click to open one of the existing races, then in the popups right side list.. right-click and select NEW. Enter a new form ID, click OK, then close the window and save the plugin. Then you can go back in and edit it, give it a name, and add any custom parts like hair, eyes, meshes, etc... To make the race available to the player, makes sure to check the "playable" checkbox on the first tab. The face that's defined on the FaceGen Race and FaceGen Data tabs, there's one for each gender, will become the default face of that race.. it's like default facial characteristics. The geck will show everyone as a member of your new race until you select an NPC to be part of it and save the plugin, after that it'll only show who's really in it.