Here are a number of quotes, some with a physical description, and some with a more complete character description:
This quote tells us about Scout's behavior as a young child.
"Scout yonder's been readin' ever since she was born, and she ain't even started to school yet."
The next two quotes indicate that Scout is average to tall for her age, as she is bigger than both Dill and Walter Cunningham. The second quote also shows that Scout is impetuous.
"Dill was a curiosity. He wore blue linen shorts that buttoned to his shirt, his hair was snow white and stuck to his head like duckfluff; he was a year my senior but I towered over him."
"Catching Walter Cunningham in the schoolyard gave me some pleasure, but when I was rubbing his nose in the dirt Jem came by and told me to stop. "You're bigger'n he is," he said. "He's as old as you, nearly," I said. "
This quote describes Scout's dress at the ladies' auxiliary meeting.
"I was wearing my pink Sunday dress, shoes, and a petticoat, and reflected that if I spilled anything Calpurnia would have to wash my dress again for tomorrow."
Also from that meeting, we have Scout's reaction to the world of women vs. men, which tells us about her character as a honest and straightforward person.
"There was no doubt about it, I must soon enter this world, where on its surface fragrant ladies rocked slowly, fanned gently, and drank cool water. But I was more at home in my father's world. People like Mr. Heck Tate did not trap you with innocent questions to make fun of you; even Jem was not highly critical unless you said something stupid. Ladies seemed to live in faint horror of men, seemed unwilling to approve wholeheartedly of them. But I liked them. There was something about them, no matter how much they cussed and drank and gambled and chewed; no matter how undelectable they were, there was something about them that I instinctively liked... they weren't- "Hypocrites, Mrs. Perkins, born hypocrites," Mrs. Merriweather was saying. "
This final quote is from her walk home from Boo's at the end, and shows us that she is maturing - but is still a young girl.
"As I made my way home, I felt very old, but when I looked at the tip of my nose I could see fine misty beads, but looking cross-eyed made me dizzy so I quit. "