This can be in a new page, or inserted into an existing page.
Open up the page for editing, and then click ‘Add Media’. In the top left of the new screen is the option to create a gallery. You can then select pictures that have already been uploaded to the site (less likely), or click upload files to upload new files to add to the gallery (more likely).
The files that are selected for the gallery appear as little images at the bottom of the window. When you have all the images, click ‘Create a new Gallery’.
You are now in the ‘edit gallery’ mode where pictures can be captioned and repositioned (by dragging) before clicking ‘Insert Gallery’, which puts the gallery onto the page. You are now back to editing the page, where heading text etc can be added before publishing the page.
Editing a picture gallery
Start editing the page and click on the gallery object. Two icons then appear, one for editing the gallery and one for deleting it. Click the edit gallery’ button and you can rearrange the pictures and change the captions. There is an ‘add to gallery’ on the top left for adding additional pictures.