A post represents a single image that's been uploaded. Each post can have several tags, comments, notes, and artist commentaries. Each post may also belong to multiple pools. If you have an account, you can also add a post to your favorites.
Searching for posts is straightforward. Simply enter the tags you want to search for, separating tags by spaces and words within tags by underscores. For example, searching for blonde_hair blue_eyes will return every post that has both the blonde hair tag and the blue eyes tag.
Be aware that tags for characters and series are usually known by their original Japanese names, not their English names. For example, the tag on Danbooru for The Melancholy of Haruhi Suzumiya is Suzumiya Haruhi No Yuuutsu. See help:tags for more information.
Danbooru also offers many metatags that let you further refine your search. Metatags allow you to query on things like image width, height, score, uploader, upload date, and more. Consult the cheat sheet for a complete list of what you can do.
Finally, note that Members are limited to two tags per search. See help:users for details.
In both the post listing page and on individual post pages you'll notice a list of tags with links next to them. Here's an explanation of what the links are:
This links to the wiki page for the tag. If the tag is an artist type, then you'll be redirected to the artist page.
This adds the tag to the current search.
This adds the negated tag to the current search.
The number next to the tag represents how many posts there are. This isn't always the total number of posts for that tag. If you're searching for a combination of tags, this will be the number of posts that have the tag AND the current tag query. If you're not searching for anything, this will be the number of posts found within the last twenty-four hours.
Some tag links may be colored green, purple, or red. Green means the tag represents a character. Purple means the tag represents a copyright (things like anime, manga, games, or novels). Red means the tag represents an artist.
When you're not searching for a tag, by default the tag list will show the most popular tags within the last three days. When you are searching for tags, the tag list will show related tags, sorted by relevancy.
Gold and above users will notice a menu labeled "Mode" in the sidebar on the main listing page. This menu lets you make several changes without ever leaving the listing page. Simply select an option and whenever you click on a thumbnail, the action will be performed in the background.
This is the default mode. Whenever you click on a thumbnail, you'll go to that post.
Whenever you click on a thumbnail, an edit box will appear. Here you can easily change the post's tags from the listing page without opening the entire post.
Write a tag script into the text box that appears, and it will be applied when you click on the thumbnail of a post. This allows you to quickly add or remove tags to many posts at once. See help:tag scripts for details on creating tag scripts.
Whenever you click on a thumbnail, that post will be added to your list of favorites.
Whenever you click on a thumbnail, that post will be removed from your list of favorites.
Whenever you click on a thumbnail, that post will be rated safe.
Whenever you click on a thumbnail, that post will be rated questionable.
Whenever you click on a thumbnail, that post will be rated explicit.
Whenever you click on a thumbnail, that post will be voted up.
Whenever you click on a thumbnail, that post will be voted down.
Lock rating (Builders and above)
Whenever you click on a thumbnail, that post will be rating locked (no one will be able to change the rating).
Lock notes (Builders and above)
Whenever you click on a thumbnail, that post will be note locked (no one will be able to edit notes for that post).
Approve (Janitors and above)
Whenever you click on a thumbnail, that post will be approved.
In the listing page, you will notice that some thumbnails have a border. The meaning of this border depends on the color.
The post was flagged for deletion.
The post is pending moderator approval.
The post is deleted.
The post has child posts.
The post has a parent.