WordPress comes with built-in gallery functionality – you can add several images to a post and show them as a gallery.
Step 1: Login to admin area
Step 2: Go to Posts and Add New.
Step 3: Click the Add Media button in the WYSIWYG editor menu and upload the images that will be shown in the gallery.
Step 4: 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.
Step 5: To insert the gallery to your post, click Insert Gallery.
Step 6: Publish your post and you will be able to see your gallery in the new post on your WordPress blog.