"Vocation" means a "call." Your vocation is what God calls you to do with your life.
Everybody is called by God to know, love and serve him. The difference is how each one does this.
Individual vocations vary between being single, married, consecrated, religious or a priest. However, we usually use "Vocation" to mean a call to the consecrated, religious or priestly life.
In the one life God gave you to live, you have one fundamental purpose, to fulfil the will of God, because this is the key to your true destiny, eternal happiness.
God gives each one of us a particular mission in life. As we grow and life progresses, he makes it known to us, usually in indirect ways, more as an invitation than an imposition.
Discovering and ultimately following your vocation gives the greatest glory and praise to our Creator. It is what we were meant to do.
"Take up your cross and follow me" (Mark 8:34).