Adding Next Gen Gallery photos to gallery and then adding to page
Hover over 'Gallery', click on 'Add Gallery / Images'
Select required gallery from the dropdown,Or create a new one.Click on add files and select required images, click 'Start upload'.
Go To Pages => Edit Page
Select required page
Add shortcode to page[nggallery id=4]
Change ID to the id of the gallery.
Click the 'Update' button and voila!