A post represents a single file that's been uploaded. Each post can have several tags and comments. If you have an account, you can also add a post to your favorites.
Searching image captions is pretty straightforward. Simply enter the words you want to search for, separated by spaces. Images will be returned that contain the words entered into the search query.
Searching for tags is can be slightly more tricky. Simply enter the tags you want to search for, separated by spaces. For example, searching for animal clothes will return every post that has both the animal tag AND the clothes tag.
Currently, to search for terms with more than one word you will need to use underscores instead of spaces. For example, to search for the term animal clothes as a single idea, you need to type animal_clothes into the search box. I am looking into ways to make this slightly more intuitive
In both the listing page and the show page you'll notice a list of tag links with characters next to them. Here's an explanation of what they do:
When you're not searching for a tag, by default the tag list will show the last few images added to the database. When you are searching for tags, the tag list will show related tags, alphabetically.
As a defaults setting, all Not Safe For Work (nsfw) images are hidden and must be selected to be shown. By registering (for FREE, mind you) you can select your default content filtering by choose to show only 'safe' or 'questionable' content. Or, you can select for nsfw content to be freely shown. Also, as a member, you can blacklist particular keyterms preventing them from being seen as well.