Thousands gathered at the venue to listen to Obama in an event moderated by actress Tracee Ellis Ross. Some attendees came from other states.
"It's such an honor. Michelle Obama is an icon," Nicole Vasquez of Redondo Beach said.
The former first lady talked about her time in the White House and about her childhood growing up in Chicago's South Side, where she said she preferred to be by herself, recalling her mother insisting she go outside with the neighborhood kids.
"That's where I describe my first fight that I had because there was the mean girl who just seemed annoyed with me," Obama said. "I was like, 'See, this is why I don't want to be outside.'"
The Forum was Obama's second stop in her 12-city book tour promoting her memoir, "Becoming."
The tour began earlier this week in Chicago on stage with Oprah Winfrey.
Her memoir left a lasting impression on Beth Martinez, who celebrated her birthday by attending the event.
"She remembers her Chicago roots, and her being so candid about her marriage," Martinez said.
Organizers said Obama gave away hundreds of free tickets to her book tour so that people from underprivileged communities could attend.
Earlier in the day, the former first lady stopped by Para Los Ninos near Skid Row to read some of her favorite children's books.
She also brought the young readers books as gifts.
Obama told the crowd growing up she was allowed to have a voice. Her parents treated her as an equal.
Other stops in her book tour include Detroit, Boston and Paris.