To search under a tag, you can either click on the tag, or type [<tag-name>] in the search field. Once you get to the search returns page, the advanced search options link appears with the guidelines for more sophisticated searches. However, you don't need that link to appear on the page in order to use those options; from any old page you can type [<tag-name>]+answers:1 in the search field to get all the threads tagged with that topic that have at least one answer. For example, here are the questions tagged under clustering that have one or more answers.
(By the way, did you notice the meta thread I posted that was inspired by your last meta-Q? That might help you to navigate CV. Enjoy!)