Those who are led by the Spirit of God are the sons (and daughters) of God. It is through his leading that you begin to do the works of God. If by his leading you end up in part-time or full-time ministry, you can they say you were called.
It is like becoming a Christian. God’s Spirit had been preparing you for salvation for days, months or years. When the time was right you heard a message and the Spirit witnessed with your spirit that it was true. You accepted the Lordship of Jesus over your life.
There will come moments when the Spirit says in your heart, “do this”, and it will be a ministry of service. That is the call. It can be a onetime affair up to a lifetime ministry.
🙂