If you haven’t already installed it, install the NextGen Gallery Plugin
Under the gallery tab on left, click on Add gallery/images
On initial set up you will need to add a gallery so click add new gallery at the top
Enter the name of the gallery e.g. frontdoors then click add gallery
To add images
Still on the add gallery/images tab choose upload images
Click select files & choose files from your computer (you can do multiple uploads) and click open
Tick the scale images to…. Box
And then choose the gallery you want them to go into & then upload images
To manage the images (e.g. rename them)
Click on manage gallery on the left tab & then on the gallery you want to edit photos in
To change the names type in the text into the top box next to the image
Click on save changes
To add a gallery into a page/post
In the main body of a post or page click on the NextGEN icon
A box will pop up with various choices
Select the gallery/album/picture you want to insert and then how to show it and Insert and you will see the shortcode in your post.