Watch these USA Swimming videos as an introductory course to officiating.
You can shadow another official to learn and train during a swim meet.
Our "uniform" is a white shirt (usually a polo) and navy blue shorts. You'll get wet, so wear shoes that don't slip. Also recommended: a hat and sunglasses.
Don't worry. The job might seem like a lot to learn. It's an on-the-job training, and it will all make sense when you shadow another official around for a bit.