How do Jehovah's Witnesses understand Hebrews 1? Hebrews 1:4–14 contrasts Jesus with the angels.  How do groups like Jehovah's Witnesses, who see him as an angel, understand these verses?
The Jehovah’s Witness understanding is based upon their doctrine of the Son of God having been created by Jehovah God as his first created creature. They say the first thing Jehovah created was the Archangel, Michael, who also has the name, the Word of God. This Archangel then created all the other angels, this universe, this planet and all life on it, with Jehovah’s enabling. He later became the man, Jesus Christ. It is Michael the Archangel who will return in the future, they claim.

This is what their ‘What Does The Bible Really Teach?’ book (2009 printing) says about Jesus as Michael the Archangel (pages 218-219): 


  "Likewise, the Bible indicates that Michael is another name for Jesus
  Christ, before and after his life on earth… Moreover, Jesus is linked
  with the office of archangel… Thus the voice of Jesus is described as
  being that of an archangel. This scripture therefore suggests that
  Jesus himself is the archangel Michael… Since God’s Word nowhere
  indicates that there are two armies of faithful angels in heaven – one
  headed by Michael and one headed by Jesus – it is logical to conclude
  that Michael is none other than Jesus Christ in his heavenly role."


Their “Insight On The Scriptures” Vol. II page 394 (published 1988) uses Revelation 19:11-16 to conclude 


  “that Michael is Jesus Christ, since Jesus is Jehovah’s appointed
  King, commissioned to destroy all the nations at Har-Mageddon.”


So Jehovah’s Witnesses believe it will be Michael the Archangel who heads up the angelic armies at the battle of Armageddon. All of the foregoing establishes clearly their belief that Jesus is actually a created angel.
Now it becomes obvious why their New World Translation of the Holy Scriptures renders Hebrews 1:6 as, 


  “But when he again brings his firstborn into the inhabited earth, he
  says, ‘Let all God’s angels do obeisance to him’.”


Angels must not receive worship - a clear teaching in the Bible that Jehovah' Witnesses agree with. That is because angels are created and creatures must not be worshipped. Now, I quoted that verse from their 1984 edition. Yet their 1969 ‘Kingdom Interlinear Translation of the Greek Scriptures’ says, 


  ‘…let all God’s angels worship him’.”


I do not know what year that transition from ‘worship’ to ‘do obeisance to’ was made, but it seems that the change was made to prevent their version of the Bible from even hinting that God would have his angels worship Christ.

In their New World Translation, every time the word for worship applies to Jesus, they render it as bowing down with respect. But every time the word applies to Jehovah God, they render it as worship. An article on this view of Jesus is found here

The Jehovah's Witnesses say that angels are merely to bow down respectfully before Jesus but deny that this amounts to worship. That is how they see Hebrews chapter 1.  Yet verse 3 presents a theological problem to them, which they don’t seem to have taken account of. Their KIT renders it as, 


  “[Jesus] is the reflection of [God’s] glory and the exact
  representation of his very being.”


Well, if the Jehovah’s Witness Jesus has the being of an angel, they are effectively saying that Jehovah God also has the being of an angel. However, that requires another question as you did not seem to include verse 3 in your question, asking specifically about verses 4 to 14.