Angels

 When God said, “Let us make man in our image” who was God speaking to?

God was speaking to the angels.

"And God said, Let us make man in our image, after our likeness... " - Genesis 1:26 

Where does it say in the Bible that God and the angels make appearances in the form of man?

The Bible tells us that three men appeared to Abraham. We find them to be the LORD and two angels. 

"And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day; And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground," - Genesis 18:1-2 

You can read in the rest of chapter 18 how he entertained them, and the conversation they had. After a certain point, the two angels left to go to Sodom.

"And the men rose up from thence, and looked toward Sodom: and Abraham went with them to bring them on the way." - Genesis 18:16 

The third man remained to finish talking with Abraham. Who was this third man?

"And the men turned their faces from thence, and went toward Sodom: but Abraham stood yet before the LORD." - Genesis 18:22 

Where in the Bible does it say that the other two men that left Abraham and went to Sodom were angels? 

It tells us this in the first verse of the next chapter:

"And there came two angels to Sodom at even; and Lot sat in the gate of Sodom: and Lot seeing them rose up to meet them... " - Genesis 19:1 

Because angels appear to us in the image of man, we can understand this verse:

"Be not forgetful to entertain strangers: for thereby some have entertained angels unawares." - Hebrews 13:2 

Abraham and Lot entertained angels unawares because the angels appeared to them as men.

"And he said, Behold now, my lords, turn in, I pray you, into your servant's house, and tarry all night, and wash your feet, and ye shall rise up early, and go on your ways... and he made them a feast, and did bake unleavened bread, and they did eat." - Genesis 19:2-3 

We too may have entertained angels unawares.