Ok simply put. How do you know for certain if the Lord is calling you to do something?
God speaks to our hearts, [Our Spirit], Not our minds. 1 Cor 2: 10--14.
Mankind is Spirit souls and body, With our body, we contact the physical realm , with the soul, we contact the mental realm,
And with the spirit we contact the spirit realm.
The Bible calls the inward man, [The spirit], The belly, Prov 20: 27. Jn 7: 37--39. So if you will be sensitive to what your inward man is saying, you will hear and know the will of God for your life.
It can come by an inward witness, [It's just a knowing]. Acts 14: 8--10
Or it can come by the still small voice, [In your spirit]. 1 Kings 19: 11---12
Or it can come by the Holy Spirit speaking to you, [This voice has more authority, and is more clearer]. Acts 8: 29.
Acts 9: 10--16.
They are the main ways that God leads us.
Jesus said His sheep will hear His voice. Jn 10: 27. Paul said the children of God are led by the Spirit of God, And God speaks Spirit to Spirit. Rom 8: 14
James said if we lack wisdom, [Insight to future events], let us ask God who gives it to us. James 1: 5.
So ask God for guidance, Then keep thanking Him for wisdom leading and guidance.
The Prophets and Teachers in Church at Antioch, Acts 13: 1--3 were praising, thanking and worshiping God, and it created an atmosphere where God could speak to them.
Paul said don't be unwise, but understand God's will, Then he tells us how we can understand God's will.
"Be filled with the Holy Spirit". Eph 5: 17--18.
Speaking in tongues will help, as one of the operations of tongues is, Our spirit praying 1 Cor 14: 14.
And 1 Cor 14: 2 says when we speak in tongues, we speak mysteries, [Hidden secrets], Not hidden from us, But hidden for us, And one way to have these secrets revealed, is by praying in tongues. 1 Cor 14: 13. So if God said we can interpret tongues, that means we must know what He is saying, and in the same way, God can reveal His plans for us, as we pray in tongues.