WordPress comes with a built-in gallery feature; where you can add several images to a post/page and show them as a gallery. You can view the gallery live in our demo site
1. Click on Add Media button and it will pop-up the media uploader
2. Click on Create Gallery
3. You can choose to upload files from your computer or choose from Media Library (for existing images that you’ve uploaded)
4. Click to select the images that you’d like to insert in the gallery
5. When you’re selected the images, proceed to click Create a new gallery button
6. At this stage you can drag and drop the images to rearrange the order
7. Under Gallery Settings, please ensure that you have the images link to Media Files (select the drop-down). That way if you click on the gallery image, it will open (pop up) in a lightbox instead of open in a new page. You can also select the number of thumbnail column shows in a row.
8. When you’re done with all the setting, click on Insert Gallery button. Just click Update or Publish on your post/page, and the gallery will be added to the live site.
To change thumbnail image size, go to Settings – Media – Edit the Thumbnail dimension (width and height) depends on your preference. Next, install and run Regenerate Thumbnails Plugin to regenerate the new thumbnail size.