The word discernment is often used to describe how a person comes to know their vocation. There are many voices telling us what we should or should not do with our lives, but which one is God's? If you want to recognize His voice, to discern it from all the others, you need to get to know Him. You get to know Him by spending time with Him in prayer, reading scripture, through the sacraments and though each other. 

Six Ways to Discern
 

1. Prayer. Prayer is a conversation with God- not just saying prayers, but speaking to the Lord from your heart. 
2. Sacraments. The soul is the window through which we can see God and hear his voice. If the window is dirty because of sin, it must be cleaned through confession so that we can be in union with God. 
3. Good information. It is impossible to discern a vocation without good information. Find good information online then take what you have learned back to prayer. 
4. The Blessed Mother. Mary is the ultimate example of openness to the will of God. Pray to Mary asking her to intercede for you as you discern your vocation. 
5. Go on retreat. Miracles happen on retreats! One of the surest ways to discover God's plan for you is to enter into silence and prayer over an extended period. 
6. Get advice. Don't try to discern your vocation alone, without the help of the Church. Talk to others about your discernment.