A loquacious person talks a lot, often about stuff that only they think is interesting. You can also call them chatty or gabby, but either way, they're loquacious.
Whenever you see the Latin loqu-, you can be sure that the word has something to do with "talking." So a loquacious person is a person who talks a lot, and often too much. Sitting next to a loquacious person at a dinner party can make dinner a real drag. Of course, if you've got nothing to say, a loquacious person might make a good dinner companion, because they'll do all the talking. All you will have to do is smile and eat.