in chapter 19 what happened during toms questioning

Quite a bit, as this is the focus of the whole chapter. Here is a summary:

Tom Robinson is called to the witness stand. He tries to put his left hand upon the Bible, but it is a futile effort, as his left arm is entirely non-functional. The arm simply slips off the Bible again and again. Finally, the judge tells him his effort is sufficient and he can take the stand. Atticus questions Tom, first asking whether he has ever been convicted of a crime. Tom explains that he was once convicted for fighting because he could not pay the fine that would have released him. In an aside, the narrator explains that Atticus is showing how honest Tom is and that he has nothing to hide from the jury. Next, Tom gives his account of the Ewell incident.

In Tom's version, he says he passed by the Ewell house every day on his way to work at Mr. Link Deas's farm, where Tom picks cotton and does other farm work. Tom confirms that one day last spring, Mayella asked him to chop up an old chiffarobe with a hatchet, but that was long before the November day in question. After Tom performed that favor for her, Mayella often asked him to help her with odd jobs around the house as he passed by. She offered him a nickel the first time, but he refused payment, knowing that the family had no money. He said he helped her out because she didn't seem to have anyone else to help her, and that he never went onto the Ewell property without being invited. Scout thinks about how lonely Mayella is - she's so poor that white people won't befriend her, but black people will avoid her because she's white.

Atticus asks about the events on November 21 of that year. Tom says that he passed the Ewell house as usual, and everything seemed very quiet. Mayella asked him to come inside and fix a broken door, but when he got inside the house, the door didn't look broken. Then, Mayella shut the door behind him and said she had sent the children to town to get ice cream, having saved for a very long time to be able to give each child a nickel. Tom starts to leave, but she asks him to take a box down from on top of another chiffarobe. As Tom reached for the box, Mayella grabbed him around his legs. He was so startled that he overturned a chair. Next, she hugged him round the waist and kissed his cheek, and as Tom explains, said that, "she never kissed a grown man before an' she might as well kiss a nigger. She says what her pap do to her don't count." Mayella asks him to kiss her back, and Tom asks her to let him out of the house. However, her back is to the door, and he doesn't want to force her to move. He knows that as a black man, if he lays a hand on her he could later be killed. Then Mr. Ewell arrives, happens upon the scene, calls his daughter a "goddamn whore," and tells her he will kill Tom. Tom runs away in fear.

Mr. Gilmer questions Tom next, and he does so fairly aggressively, addressing him only as "boy". Mr. Gilmer tries to get at Tom's motivations for helping Mayella, insinuating that he must have had ulterior motives for helping her. Tom finally says he just tried to help because he felt sorry for her, which stirs up the audience considerably, as it is unacceptable for a black man to feel sorry for a white woman. Mr. Gilmer asks whether Tom thinks Mayella was lying about asking him to chop up the chiffarobe in November. Tom avoids a potential trap by saying he thinks Mayella must be, "mistaken in her mind" about this and everything else. Mr. Gilmer asks why Tom ran if he had a clear conscience, and Tom said he was afraid of being tried in court, not for what he did, but for what he didn't do.

Atticus asks about the events on November 21 of that year. Tom says that he passed the Ewell house as usual, and everything seemed very quiet. Mayella asked him to come inside and fix a broken door, but when he got inside the house, the door didn't look broken. Then, Mayella shut the door behind him and said she had sent the children to town to get ice cream, having saved for a very long time to be able to give each child a nickel. Tom starts to leave, but she asks him to take a box down from on top of another chiffarobe. As Tom reached for the box, Mayella grabbed him around his legs. He was so startled that he overturned a chair. Next, she hugged him round the waist and kissed his cheek, and as Tom explains, said that, "she never kissed a grown man before an' she might as well kiss a nigger. She says what her pap do to her don't count." Mayella asks him to kiss her back, and Tom asks her to let him out of the house. However, her back is to the door, and he doesn't want to force her to move. He knows that as a black man, if he lays a hand on her he could later be killed. Then Mr. Ewell arrives, happens upon the scene, calls his daughter a "goddamn whore," and tells her he will kill Tom. Tom runs away in fear.

Mr. Gilmer questions Tom next, and he does so fairly aggressively, addressing him only as "boy". Mr. Gilmer tries to get at Tom's motivations for helping Mayella, insinuating that he must have had ulterior motives for helping her. Tom finally says he just tried to help because he felt sorry for her, which stirs up the audience considerably, as it is unacceptable for a black man to feel sorry for a white woman. Mr. Gilmer asks whether Tom thinks Mayella was lying about asking him to chop up the chiffarobe in November. Tom avoids a potential trap by saying he thinks Mayella must be, "mistaken in her mind" about this and everything else. Mr. Gilmer asks why Tom ran if he had a clear conscience, and Tom said he was afraid of being tried in court, not for what he did, but for what he didn't do.