Confirmation
You receive the strength of the Holy Spirit to live your faith and to make it known.
The sign
The bishop anoints your forehead with sacred chrism, a perfumed oil, and says: "Be sealed with the Gift of the Holy Spirit."
Who gives it
Normally, the bishop. A priest can also confirm with the bishop's permission.
How many times
Only once in a lifetime.
What the Bible says
Acts 8:14-17
14Now when the apostles, who were in Jerusalem, had heard that Samaria had received the word of God, they sent unto them Peter and John. 15Who, when they were come, prayed for them, that they might receive the Holy Ghost. 16For he was not as yet come upon any of them; but they were only baptized in the name of the Lord Jesus. 17Then they laid their hands upon them, and they received the Holy Ghost.
Douay-Rheims Bible (Challoner revision), public domain.
Source: Catechism 1285, 1300, 1304, and 1312-1313