OURTorah: A Yoetzet Halachah is a woman who spends several years learning Hilchos Niddah and has a broad knowledge of all the relevant Halachos and Sugyos. They do not Pasken debatable Shailos (they have a Rav/Posek they forward those on to) but anything that is black and white they can answer. The reason for this is that many women feel very uncomfortable asking detailed Niddah Shailos from a man and showing them Maros issues.
It also happens that, since Yoatzot are among the more knowledgeable women in a community, they will become teachers and lead classes for other women. However, that is not part and parcel of the job. It’s just a side-effect of being more knowledgeable.
The purpose is not to Pasken or be Rabbis. It’s to provide a more sensitive and Tznius alternative to a situation that is uncomfortable for many women (not to say that asking Niddah Shailos isn’t Tznius, but it certainly is in the eyes of many). There are many women who would just be Machmir on everything and make Taharas HaMishpacha an unbearable proposition because they are too uncomfortable to ask Shailos to a male Rav (or who would be incorrectly Meikil because they would guess because they’re too uncomfortable). Yoatzot provide a tremendous service to their communities by being available to answer such questions in a much less uncomfortable way.