1) From the back end "administrator" interface, go to Components -> Ignite Gallery.
2) Click "Manage Images" in the row with the category that is being used for the gallery you'd like to edit.
In the left side "Category" should be highlighted in blue indicating you are in Category list view.
3) From the gray box in the center, add images.
Once the image shows in the list and is "Published" (should show green check box rather than red circle), the image should show in the gallery.
4) Choose the edit link in the image description to edit the image details.