You can only add one gallery per page. But you can organize a single gallery into categories.

1. Click 'New Category'
    
2. Add the Category
   • Name: Will appear to the public.
   • Description: Will appear to the public below the category title.
   • Priority: Order the categories.
      
3. Now go to Galleries > View Gallery X. Click on a photo and choose the 'Under Category' dropdown.