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.

There are several ways to add video or audio files to your WordPress posts. If the media is in the supported oEmbed options list (including YouTube, Vimeo, Soundcloud, etc.), your first option is simply to paste the link into your post content. WordPress will automatically embed the media for you.

Another option is, if your WordPress theme includes built-in "Post Options," you can add video or audio as featured media (instead of a featured image). If this option is available in your post, simply paste the media link or upload your own mp3 or video file.

To select categories and add tags to your post, use the meta box on the right side when creating the post. You can choose from existing categories and the most commonly used tags, or create new categories and tags.

When writing a post, click the "Set Featured Image" link in the "Featured Image" meta box. This will open your media library. Select an image or upload a new one, then save it.

Typically, your image will be displayed using its default size, but depending on your theme, there may be additional cropping (cropping the image based on the theme's designed height/width) or display options (such as stretching, covering, etc.). Please refer to your theme's documentation to find these settings, although they are usually located in the customizer or theme panel.

Post formats are styles for blog posts, typically based on the media/content within the post (such as images, galleries, videos, quotes, etc.). When creating a blog post, you can find this option in the "Format" meta box on the right side of the screen. Learn more in our guide to post formats.

To create a new WordPress post, first log in to your WordPress installation, then go to Posts > Add New. Here, you can add the post title, content, excerpt, and more.