It doesn't flare the teeth, in fact, my teeth are angled down for the first time in my life! They used to flare out in order to meet my bottom teeth.
How it works: your palate is split open during surgery by the doctor in a few key places so that it can open up, but is still stable. Then, depending on how much your palate needs to be widened, you turn a key every day for a few weeks and a gap slowly begins to form. Once your palate is widened enough, you stop turning the key and the expander stays in to keep everything as stable as possible. Once your palate has begun to fuse again and everything isn't wiggly anymore, the expander is removed and then the orthodontist can begin to bring the gap back together.
Does this make sense?!