Cross candles have multiple uses: The image of the cross is reminiscent of the domination and dominion that Christ has over the earth. It can be used for spiritual protection, blessing, healing, strength, mastery, power, success, and more. It can also be used for commandment, domination, and besting opponents. 
One way to use a cross candle is to anoint it in Fiery Wall of Protection Oil, and inscribe your name into it, while praying Psalm 25 for spiritual protection. Another way to use the candle is to anoint it in Domination Oil, and put the candle on top of a photo of the person you want to dominate while reciting Psalm 118.