# the brightness of God's glory, the exact representation of his being

"the light of his glory." God's glory is associated with a very bright light. The author is saying that the Son embodies that light and fully represents God's glory. The phrase "the exact representation of his being" is similar in meaning to "the brightness of God's glory." Alternate translation: "glory and is just like God" or "glory, and what is true about God is true about the Son"

# the word of his power

"his powerful command" 

# After he had made cleansing for sins

"After he had finished making us clean from sins" or "After he had finished purifying us from our sins" 

# he had made cleansing for sins

"he had made it possible for God to forgive our sins" 

# he sat down at the right hand of the Majesty on high

"he sat down at the place of honor and authority beside the Majesty on high"

# the Majesty on high

"God Most High"