A small white badge was pinned to her lapel bearing her prisoner number, 503.
Park, handcuffed and in a navy suit, appeared at the Seoul Central District Court escorted by correctional officials.
She is expected join the former president in court on Tuesday, and judge Kim Se-yoon is expected to decide whether to try them together or to split Park's and Choi's cases.
Park said little during the first day of her trial, conferring quietly with her lawyer Yoo. Park and Choi had been a friend for some four decades, but they did not acknowledge each other in the courtroom.
South Korea's former President Park Geun-hye (C) arrives for a trial at the Seoul Central District Court in Seoul, South Korea, on May 23, 2017.
"But outside court there was a very vocal crowd who believe that their former president has been framed".
During a televised apology in October, Ms. Park described Ms. Choi as a close friend who "helped her during hard times in the past". "But those supporting this process, say while this is partly about [Park], it's important for South Korean democracy that this process goes ahead".
She denied all the charges against her, and her lawyers told the court she could not benefit personally from the foundations.
Park was accused of being unduly influenced by her longtime friend and adviser, Choi Soon-sil, who is also on trial for abuse of power and fraud.
At the hearing, Ms. Park denied all charges, and Ms. Choi has previously denied wrongdoing.
At the first hearing, a judge asked Park about her identification including address, occupation and a date of birth.More news: North Korea says ready to deploy, mass-produce new missile
Park has previously blamed Choi for abusing their friendship.
Park isn't the first South Korean president to face trial.
The trial is expected to last for several months.
And last week, two plastic surgeons who treated the image-conscious former president - including one who injected her with human placenta extracts - were convicted of lying about having treated her. A top court ousted her from office.
Her confidante Choi Soon-sil is seated far right.
Tuesday's court session was her first public appearance since then.
Some 500 people lined up on Friday at Seoul court to apply for one of 68 courtroom seats to get a ringside view. That month, Ms. Choi, who has been accused largely of meddling in state affairs, was indicted on additional charges, including colluding with Ms. Park to extract money from the Lotte and SK business empires.
Park's removal from office cleared the way for criminal proceedings, as South Korean presidents face immunity from prosecution.
Park met Samsung's Lee in July and told him she hoped the succession at the world's biggest smartphone maker "would be resolved smoothly under her government", asking him to support the foundations, according to prosecutor Hwang Woong-Jae.
Park is also accused of leaking state secrets by giving Ms Choi access to her work - including asking her to edit her speeches - and of running a blacklist of media figures who were to be barred from receiving state support because they had been critical of her government.