To easily add several images to a post and show them as a gallery in WordPress, go to your blog’s admin area and click Posts > Add New.
Click the “Add an image” button in the WYSIWYG editor menu and upload your images.
Then click Save all changes. A Gallery tab will appear. Click on the tab to arrange your images and choose your settings. When you are done, click Insert Gallery.
When you publish your post, you will be able to view your gallery.