You'll find ticket machines at every station on the Red Line, as on other lines of the subway system in Los Angeles. First buy a TAP card, which looks like a credit card and costs $1. The machine prompts you to add value to the card. For $5, you can purchase an all-day ticket ($1.80 for seniors). It's worth getting an all-day ticket if you're going to use the Red Line as a multi-site art gallery.
More information: www.publicartinla.com/Metroart/RedLine and www.metro.net.