What does the Church teach on angels? The Catechism of the Catholic Church (CCC) is quite clear about the existence of angels: 

“The existence of the spiritual, non-corporeal beings that Sacred Scripture usually calls “angels” is a truth of faith. The witness of Scripture is as clear as the unanimity of Tradition. St. Augustine says: “‘Angel’ is the name of their office, not of their nature. If you seek the name of their nature, it is ‘spirit’; if you seek the name of their office, it is ‘angel’: from what they are, ‘spirit’, from what they do, ‘angel.'” With their whole beings the angels are servants and messengers of God. Because they “always behold the face of my Father who is in heaven” they are the “mighty ones who do his word, hearkening to the voice of his word”. As purely spiritual creatures angels have intelligence and will: they are personal and immortal creatures, surpassing in perfection all visible creatures, as the splendor of their glory bears witness” (CCC 328-330).

The word "angel" comes from the Latin word angelus and means “one going” or “one sent.” In other words, a messenger. So, it isn't describing a being as much as a function: what these individuals are doing as part of God's plan. Often that plan includes making humans aware of what God expects of us, so he sends us beings that we call angels. 

The archangels had very specific missions in Scripture:
St. Michael appears in Daniel’s vision as “the great prince” who defends Israel against its enemies; in the Book of Revelation, he leads God’s armies to final victory over the forces of evil. Devotion to Michael is the oldest angelic devotion, rising in the East in the fourth century. The Church in the West began to observe a feast honoring Michael and the angels in the fifth century. Pope Leo XIII promulgated the "St. Michael Prayer" which is said at Visitation and other parishes immediately following Mass.
St. Gabriel also makes an appearance in Daniel’s visions, announcing Michael’s role in God’s plan. His best-known appearances are encounters from the Gospel according to Luke with an old man named Zechariah, announcing the birth of John the Baptist, and a young Jewish girl named Mary, who consents to bear Jesus the Messiah.
St. Raphael is found solely in the Old Testament story of Tobit. There he appears to guide Tobit’s son Tobiah through a series of fantastic adventures which lead to a threefold happy ending: Tobiah’s marriage to Sarah, the healing of Tobit’s blindness, and the restoration of the family fortune.

Every human soul is appointed a guardian angel, following from the words of Jesus: “See that you despise not one of these little ones; for I say to you that their angels in Heaven always see the face of My Father Who is in Heaven” (Matthew 18:10), reinforced by St. Jerome in his commentary on this verse: “The dignity of a soul is so great, that each has a guardian angel from its birth” (Comm. in Matt., xviii, lib. II)

But the angels not only differ as individuals, but each angel is a different kind of being. A different, you might say, species. And so, Michael is a different kind of being from Gabriel and Gabriel from Raphael, and your guardian angel from every other guardian angel. That is, there’s something in them that we don’t know, there’s something in their nature which makes them an utterly different kind of spiritual being than every other spiritual being so that we say each angel is a species of its own kind. However, as far above human beings as angels are in power and intellect, they are never to be worshipped - that honor belongs to God the Father, Son and Holy Spirit alone. We can - and should - ask for the intercession in the same way that we may ask of saints (which, since angels are in Heaven, are all considered saints as well) until that day when - God willing - we will join the angels, united with them and with all the redeemed, in praising God: Holy, Holy, Holy, Lord God of hosts! (Isaiah 6:3, c.f. Revelation 4:8)