The captain had the look of a man who sees a ghost, or the evil one or something worse. Whatdoes this reaction tell you about the captain and does it make you understand his ways ever since he arrived at the inn?

The reaction of Captain Bill in seeing his old shipmate Black Dog shows that he is not happy about the meeting.

And looking back at his desire to be where there are only a few people around, it must be that he did not want to be discovered or his whereabouts known.

Explanation:

Robert Louis Stevenson's "Treasure Island" revolves around the adventure of Jim Hawkins and his search for the buried treasure. The main plot of the story revolves around the search for the evil pirate Captain Flint's hidden treasure.

Chapter 2 reveals the scene where Jim met "Black Dog", a former shipmate of his family's inn's guest "Captain Bill". When the captain saw Black Dog, he "had the look of a man who sees a ghost, or the evil one or something worse." And from his reaction to seeing his old mate, we can deduce that the captain doesn't like him and that they are not in good terms with one another.

Considering his 'negative' reaction to meeting his old mate, it is understandable that he had behaved the way he did, and his desire to be where there are hardly any people around.  

yes it is like you know me bro