how can i be sure

God has given each person an inner knowledge which causes them to seek after God.

Unfortunately some react negatively to this and choose to fill their lives with other things, but the gap is never filled other than the temporary satisfaction which is derived from a diversion of some description.

The simple truth is, if you choose to believe that Jesus died on the cross to pay the price for your sin and choose to follow Him, you will have the right to become a child of God.

Joh 1:12 But as many as received Him, He gave to them authority to become the children of God, to those who believe on His name,

I think the hard thing is to just believe. There is usually a battle that goes on between the head and the heart at this stage. The head deals with the logic and says "What about..." Whereas the heart says "Yes, this is what I've been looking for!"

Believing the heart in this case and choosing to follow Jesus is what is meant by the following scripture:

Luk 18:17 Truly I say to you, Whoever shall not receive the kingdom of God as a little child shall in no way enter into it.

CONFIRMATION

The beauty of finding Jesus is that the Holy Spirit bears witness with your spirit that you are a child of God (see Rom 8:16 below).

Rom 8:13 For if you live according to the flesh, you shall die. But if you through the Spirit mortify the deeds of the body, you shall live.
Rom 8:14 For as many as are led by the Spirit of God, they are the sons of God.
Rom 8:15 For you have not received the spirit of bondage again to fear, but you have received the Spirit of adoption by which we cry, Abba, Father!
Rom 8:16 The Spirit Himself bears witness with our spirit that we are the children of God.
Rom 8:17 And if we are children, then we are heirs; heirs of God and joint-heirs with Christ; so that if we suffer with Him, we may also be glorified together.

BRIDGE THE GAP

We are seperated from God by sin. The simple way to overcome this is to ask for forgiveness.

1Jo 1:9 If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.

Read the following prayer and if it is what you want to do, then pray this prayer to God:

Father, forgive me for the sin that has separated me from you.
Thank you for sending Jesus to die on the cross on my behalf.
Thank you that His sacrifice paid the price for my sin
And that because I believe this I am acceptable to you.
Lord, I give my life to you and choose to follow you from this day on.
Please give me your Holy Spirit to teach me and guide me along the way
Thank you for accepting me into your Kingdom in Jesus name
Amen

Act 2:38 Then Peter said to them, Repent and be baptized, every one of you, in the name of Jesus Christ to remission of sins, and you shall receive the gift of the Holy Spirit.

The next thing to do is to tell someone about what you have done. By telling someone you have received Jesus and have chosen to follow Him you 'seal' your conversion.

Rom 10:9 Because if you confess the Lord Jesus, and believe in your heart that God has raised Him from the dead, you shall be saved.

It is really important to find a church somewhere and get to know some Christians who will support you. The enemy (satan) will attempt to discourage you and turn you away from God. Everyone goes through difficult times and everyone needs support and encouragement from time to time.

It is also true that worshipping God together with a group of people is very special. It takes you into the presence of God like almost nothing else can.