Installing these adapters is a necessary step in NASA's Commercial Crew Program, which seeks to spur development of commercial crew spacecraft. Since the space shuttle was discontinued in 2011, NASA has had to pay Russia million to take its astronauts to the ISS. The Commercial Crew Program will give NASA cheaper options in crewed spaceflight.
The spacewalk is scheduled to begin at 8:05 a.m. on Friday, and live coverage will start at 6:30. This will be Williams' fourth spacewalk, and Rubins' first. Here is a video describing exactly what the spacewalk will entail: