In my Father’s house there are many mansions. If not, I would have told you: because I go to prepare a place for you. And if I shall go and prepare a place for you, I will come again and will take you to myself: that where I am, you also may be. John 14:2-3
It is a metaphor. Jesus has prepared a place for us in heaven. Given all the blessed perfection and joy that heaven is, the best comparison is that Jesus is going to prepare mansions for us to live in when we arrive.