WordPress comes with built-in gallery functionality – you can add several images to a post and show them as a gallery.
Step 1: To create a gallery in a new post, go to your blog’s admin area -> Posts -> Add New.
Step 2: Click the Add Media button in the WYSIWYG editor menu and upload the images that will be shown in the gallery.
Step 3: When you are ready, click Save all changes. A Gallery tab will appear and when you click it, you will be able to arrange your images and set the gallery settings. To insert the gallery to your post, click Insert Gallery.
Step 4: Publish your post and you will be able to see your gallery in the new post on your WordPress blog.