For writing a character description, you must identify many adjectives that describe a character and then provide the evidence of those descriptors.
For example, Bob Ewell is:
DUMB: Atticus easily proved that Bob was illiterate, and then that he had a limited understanding of vocabulary by positioning him to talk about what hand was his dominant hand.
CARELESS: Bob did not care enough about his daughter to call for a doctor when she was allegedly raped. A doctor could have not only attended to her pain, but confirmed the rape and helped provide evidence.
DIRTY: The scalded color of his skin revealed to a watching audience that this was a man who didn't bathe much. Not only does this suggest a hygiene problem, but it suggests a lifestyle of dirty in many other meanings of the word, like underhanded and corrupt.
Bob Ewell is on the witness stand in chapter 17, and he acts as if all he had to do that morning was show up in order to win the case against Tom Robinson. Bob Ewell is so arrogant that when his attorney, Mr. Gilmer, asks his name, Ewell flippantly remarks, "That's m'name, cap'n" (171). Mr. Gilmer is taken aback by how informally Ewell responds. It's as if this is just a game to him, which helps to point out that he is arrogant as well as uncivilized and uneducated.
Mr. Ewell doesn't answer so honorably to the next question, either. When asked if he is the father of Mayella Ewell, he responds disrespectfully with, "Well, if I ain't I can't do nothing about it now, her ma's dead" (172). Apparently Mr. Ewell thinks he's on stage for a comedy routine rather than at the witness stand for a very serious case.
Next, Atticus asks Mr. Ewell why he didn't get a doctor for Mayella on the day she was beaten and raped. Mr. Ewell responds that he's never called a doctor in his life and it would have cost him five dollars (175). Then, before Atticus gets to ask another question, Mr. Ewell asks if he's done. Again, this shows that not only is he not educated enough to understand what a cross-examination is, he thinks all he had to do was show up that day and the case would be won.
Finally, when Atticus eventually paints him into a corner with questions, Ewell gets angry and claims Atticus is the bad guy! He says Atticus has taken advantage of him. Then he won't stop retelling his story over and over again until he is excused. Angry people who are caught in lies usually turn the blame back on the other person to avoid responsibility for their words and actions, and that's just what Ewell does. He proves himself to be a liar, an abusive father, and a racist while on the witness stand.