In Ephesians 6 Paul lists all the elements of the Armor of God. The belt of truth is the first item mentioned. In order to be prepared to fight Satan you have to know the truth about Jesus Christ first. All the other “pieces” of the armor are based on that truth. You won’t have righteousness, peace, faith, salvation, or the Spirit without first having the truth, the belief in Jesus and His unselfish act on the cross.
How do you find out what that truth is?
Read Matthew, Mark, Luke, and John in the Bible. Then go into the Old Testament and look at the prophecies by Isaiah. There is no doubt that Jesus is the Messiah Isaiah told about.
Get the truth of Jesus firmly in your mind. The other pieces will follow. Then, with Jesus by your side, you can do battle against whatever Satan throws at you.
Do you have the Belt of Truth wrapped around you?