Are vocations specific or general?

No matter how good the parish school may be, a common refrain from homeschooling mothers across the country is that homeschooling is a "vocation".

I've also heard a respected theologian explain that we don't have a vocation to marriage, we have a vocation to marry, say, Beth Smith. We don't have a vocation to the priesthood, we have a vocation to be a Franciscan priest or a diocesan priest. We don't have a vocation to work, we have a vocation to be an engineer.

My question: if this is true, how do we know what our specific calling from God is? And, better, how do we teach our kids when and what to listen for?