The book of Revelation is a book of symbols. The symbol of the 7 lampstands in verse 12 is interpreted for us in verse 20 of chapter 1:
Revelation 1:12,13,20 Then I turned to see the voice that spoke with me. And having turned I saw seven golden lampstands, 13 and in the midst of the seven lampstands One like the Son of Man, clothed with a garment down to the feet and girded about the chest with a golden band.... 20 The mystery of the seven stars which you saw in My right hand, and the seven golden lampstands: The seven stars are the angels of the seven churches, and the seven lampstands which you saw are the seven churches.
The 7 lampstands represent the 7 churches to whom John would write in the first 3 chapters of the book of Revelation. The angels of these churches are either their leadership of these churches or a simple messenger from each church who would carry the words of the Apostle to them. The word "angel" in Greek means a messenger. That messenger can be either divine or human. In this case these 7 messengers were human. Because they are characterized as "stars" they are almost certainly leaders in the congregations to whom John wrote.
For a more complete discussion of the meaning of the 7 stars, please click on this link: The Seven Stars
I hope you have found this helpful.