I've just saved my draft post. But I can't publish because I don't know these things:
2. In Post Ads
3. Featured Image
4. Custom Body Class
5. Custom Post Class
6. Meta description
You can literally ignore all of these settings - they are completely optional.
For your reference, here is what each of them do:
1. Tags - These are additional ways to classify your post
For example if you have a post about dog food, the main category would be "dog food" but you can also add additional words - "tags" - to categorize the post with more details. For the post on dog food, additional tags might be something like "raw food", "Instinct", "kibble", etc...
2. In Post Ads - you only need to worry about this setting if you have configured In Post Ads to display in your posts. This box allows you to exclude certain posts.
3. Featured Image - While I do recommend setting this for all of your posts, until you have images, you can ignore it. Setting this is what makes an image show next to your posts on listing pages.
4. Custom Body Class - Ignore this! Unless you understand how to write code, you can break your whole site.
5. Custom Post Class - Ignore this! Unless you understand how to write code, you can break your whole site.
6. Meta description - This is an optional field that allows you to specify the description of your post for the search engines. This field controls how the listing of this post will appear when someone finds it while searching. It's a great place to specific keywords.
7. AddToAny - This checkbox allows you to turn of the share buttons for individual posts. It is checked by default and that's the recommended setting