Because the Holy Spirit is invisible and mysterious, we use symbols to help us capture a "glimpse" of the Spirit. Symbols such as oil, water, fire, and wind are associated with the Holy Spirit. Some of those symbols are used in the Confirmation ceremony. Oil is one of the symbols of the Holy Spirit that we use in Confirmation. When you are confirmed, the bishop will rub scented olive oil on your forehead and the two of you will have a short dialog that goes like this: Bishop: "Be sealed with the gift of the Holy Spirit."
Bishop: "Peace be with you."
You: "And with your spirit."
Watch this video to learn about the meaning of oil in our lives and in the Sacrament of Confirmation.