How does Dickens present Scrooge's character in stave one of A Christmas Carol?

Dickens presents Scrooge's character through exposition, dialogue, and point of view.  Early on in the stave, Dickens gives us some background information about the main character, referred to as exposition, including that the feeling he most cherished on the day of his sole friend's funeral was the satisfaction that he "solemnised it with an undoubted bargain" on the ceremony and proceedings.  Scrooge is further described as being unaffected by either heat or cold.  In fact, 

No warmth could warm, no wintry weather chill him.  No wind that blew was bitterer than he, no falling snow was more intent upon its purpose, no pelting rain less open to entreaty.  

Thus, we learn fairly quickly that Scrooge is uncompassionate, marked by bitterness, inexorable, and inflexible.

The dialogue with his nephew—as well as the dialogue with the two gentlemen soliciting donations for the poor—helps us to understand Scrooge's character.  He calls Christmas a "humbug," insults his nephew, and suggests that every "idiot" who goes about wishing people a "Merry Christmas" should be murdered with dessert.  To the gentlemen, he insists that he pays enough for public institutions like the prisons and workhouses (both truly terrible places), and he says that poor people should go there if they need help—a rather cruel perspective.

Finally, Dickens also uses a third-person omniscient point of view to help us further understand Scrooge's thoughts and feelings.  We do get the thoughts and feelings of many characters, and this has the effect of helping us to better understand all of them.