Celestial magic in general is the invocation of the divine power, mainly used through bargains, pleas, and favors. In it's most lowly form it can be passed off as divine miracles, in it's greatest form it resembles God's wrath.
Infernal magic is the evocation of demonic power, unlike Celestial which is gained through sacrifice of your own power or well-being. Infernal is powered through the sacrifice of others. While you could perform God's wrath with Celestial, you could theoretically raise hell with Infernal.
Both are having influence over two sides of the divine spectrum, angels, demons, Lucifer, Destruction, and Creation CAN be influenced by this magic. As it's the manipulation of their very essence, given that enough has been sacrificed of course.