To add an image gallery, you can use the built-in WordPress gallery option. Simply click the "Add Media" button at the top of your post content, then select the "Create Gallery" option. After that, select the photos you want to use and click the "Create a new gallery" button. However, before finishing and inserting, make sure to check the number of columns and the link location for the images (if you're linking to media files for a lightbox effect, or if you want the image to open in a new tab or custom URL, link to the attachment page).
The second option is to use any gallery or media options included in the theme. Some themes come with a gallery post format, and when creating a post, you'll see a "Gallery" meta box below the content. Simply use this option to "Add Images" and select the pictures you want to include in the gallery.
