NASA says that you'll need to be a US citizen with either a master's degree in a STEM field or an equivalent, such as two years of work toward the doctorate in your field, a medical doctorate or the combination of a completed test pilot school program (finished by June 2021) with a STEM bachelor's degree. You'll also need real-world experience that includes either two years of "progressively responsible" work experience or 1,000 flight hours as a pilot in command. And did we mention that you'll have to pass a long-duration spaceflight physical?
If you do pass muster, though, it's a big opportunity. Barring any changes in plans, the next two decades at NASA will be dominated by lunar and martian expeditions. And even if you don't go, this is the first call for astronauts in over four years. It's a chance to be part of a very small club that has ventured beyond Earth, even if you don't go further than the International Space Station.