The Assumption refers to the fact that Mary, being sinless at her conception and sinless her entire life, was assumed body and soul into heaven after her death. The idea of the Assumption has been around since the fourth century; the fact that no one has found, or ever noted, where Mary was buried, is another point in the doctrine's favor. If people knew that, there would definitely be a church there, and relics galore. But there's never been any evidence of the grave site.
The dogmatic declaration of the Assumption only occurred in 1950, so it's pretty "new" in that sense. But there is evidence that people believed in the Assumption, as I noted, in the early church.
It's important to note here that Mary is not God. Mary is very, very special. We do not worship Mary. To Catholics, worship is the Mass. The only person that Mass is offered to is...God. We don't say "Oh, Mary, accept our offering of bread and wine and change them into the body of your son" etc. etc. etc.
Catholics have worship, but we also have reverence and devotion. We are devoted to Mary because she is the Mother of God. She was human, like us, and she lived through many difficult things: the death of her husband, the death of her son, fleeing her country because a crazy king wanted to kill her son, not to mention having to explain a miraculous conception to her husband. To Catholics, Mary is our mother, and we come to her like we would come to our moms here on Earth.
Yes, our churches, more often than not, have statues of Mary, and pictures of her. She's one of the most common subjects in the history of art. Yes, we light candles before statues of her and statues of saints. But this isn't worship, to a Catholic. This is piety. This is prayer. We have pictures of her, and Jesus, and Joseph, and the saints, the same way people keep pictures of loved ones in their homes. We love them, and they're our examples and our helpers. When we ask for their prayers, we ask it the same way I would ask you blog readers to pray for me. Just because someone is dead doesn't mean they still don't exist.
Mary is God's most brilliant creation. (Jesus doesn't count, because....he's GOD.) But she's also the humble, believing girl from Nazareth. And she loves us all, because we are brothers and sisters of her Son. So Catholics ask us to pray for her, and we honor her with hymns and paintings and feast days. But we don't worship her. She wouldn't want us to! Mary always, always points us to her Son. If we've forgotten about her Son, we're doing it wrong. But Jesus also wants us to remember his mother. It's a two-way thing. She wasn't just the body that bore him and took care of his physical needs. She was his Blessed Mother.
The Fourth Commandment is "Honor thy father and mother." You can be sure that Jesus fulfilled this perfectly in His life. If we are to follow His example, then we are to honor His father and mother, as well. Being devoted to Mary doesn't mean being less devoted to Jesus. If anything, she brings us always closer to him.
(This was taken from Em’s post in 2016).