How to Insert a Photo Gallery into a WordPress Page or Blog Post
On the Add New Page (or Add New Post) page, click the Add an Image button.
The Add an Image dialog box appears.
Click the Gallery tab at the top of the Add an Image dialog box.
The Gallery tab appears only for posts or pages that have one or more images uploaded.
This tab displays thumbnails of all the images you’ve uploaded for your page (or post).
(Optional) In the Actions column, type the order that you want the images to appear in the gallery.
Type the number of the sequence in which you want the images displayed. For example, if you want an image displayed first, type the number 1. You can also drag and drop the images (with your mouse) in the order in which you want them to be displayed on your site.
In the Gallery Settings section, set the display options for your gallery.
Under Link Thumbnails To, select Image File (the physical image file) or Attachment Page (a page that displays only the image itself). Under Order Images By, choose Menu Order, Name, or Date/Time. Under Order select Ascending or Descending. Under Gallery Columns, select how many columns of images you want to display in your gallery.
Click the Save All Changes button.
All the changes you made to each individual image listed in the gallery are saved.
Click the Insert Gallery button at the bottom of the dialog box.
WordPress returns to the Add New Page (or Add New Post) page. WordPress inserts into your page (or post) a piece of short code (a snippet of code that WordPress uses to execute certain functions, such as the gallery display) that looks like this:
You have to switch to HTML view (click the HTML tab) to see this code.