Brittney Griner, the American basketball star detained in Russia on drug charges, told a courtroom Wednesday that she had been tossed into a bewildering legal system with little explanation of what was happening and what she might do to try to defend herself.

Ms. Griner described arriving in Russia after an exhausting 13-hour flight — and soon after recovering from Covid — and finding herself in an interrogation in which much of what was being said remained untranslated. She said she was also told to sign papers with no explanation of what they were.

It was her first court testimony about her arrest in a case that has taken on outsize importance because of the war in Ukraine.

Ms. Griner arrived with her wrists shackled in front of her. She was flanked by Russian security agents, including some wearing bulletproof vests, their faces covered by balaclavas.

The authorities detained Ms. Griner, 31, a two-time Olympic gold medalist who plays for the Phoenix Mercury, about a week before President Vladimir V. Putin’s forces invaded Ukraine in February. She was accused of having two vape cartridges of hashish oil in her luggage when she arrived at an airport near Moscow on her way to Yekaterinburg, where she plays for a team in the W.N.B.A. off-season.