On June 3, 2017 Alex Honnold free solos (climbs without ropes for protection) El Capitan, a 3,200 foot granite face in Yosemite. He went up Freerider, a 5.12d route, with a few variations in 3 hours, 56 minutes.
At the 2019 oscars Free Solo, a National Geographic Movie, documenting the climb, by filmmaker E. Chai Vasarhelyi ("MERU") and world-renowned photographer and mountaineer Jimmy Chin got an oscar for best documentary.
It documents Alex's relationship with his new girlfriend and the ethical and philosophical issues of filming a personal existential achievement. Honnold and Chin discuss things like, will filming encourage him to take unnecessary risks or disrupt his concentration leading to an accident or as Chin puts it "Falling thru a frame to his death."

See a brief history of El Capitan climbing.

He went up freerider, a route up the southwest face of El Capitan. It is very similar to the Salathé Wall. The first part on Freeblast is the same.

Crux Pitches:
At Freerider - American Alpine Club (AAC) Publications Honnold says, There had always been eight sections that I considered scary to solo.
He ranked them from 1-8. The list below is by pitch number. Alex's rank is in [ ] 1-Most difficult.

• 6 Freeblast Slab 5.11b - [2,3] Practiced >90 times
  Alex fell on the slab in preparation for his free solo, severely spraining his ankle.
  Honnold aborted here on an attempt earlier due to questionable conditions. He grabbed a bolt, and pulled through. The camera crew gave him a double-length sling and a carabiner, which he used with a munter hitch to rap from the fixed lines up to Mammoth Terraces.
  In 2018 two expert roped climbers were killed in a fall off of Freeblast. See Despite Investigation, Questions Remain Following June Deaths of Two Elite Climbers on El Capitan | REI Co-op Journal
• Slab leaving Heart Ledges 5.11c [6]
• 14 Downclimb to reach Hollow Flake 5.12a - [7] Practiced >10 times
• 19 Traverse to Monster Offwidth 5.11d [8] - Practiced >10 times
• 23 Boulder Problem 5.13a - [1] Practiced >60 times
  The Boulder Problem is a difficult sequence across thin handholds, some no wider than a pencil that are far apart. The wall is nearly vertical.
  The Boulder Problem is the single reason nobody had even considered free-soloing Freerider," says Tommy Caldwell, a climbing partner of Honnold, in a Men's Journal article. "It took Alex almost a decade to get comfortable on it. Otherwise, he'd probably have free-soloed it in 2009."
  According to Caldwell,
  "One move on this pitch is the single toughest of the climb. Honnold had to plant his left foot far out to the side, higher than waist-level, braced against the raised left edge of a crack.
  "It's almost like a karate kick," says Caldwell. From there, he would've been able to push himself up and secure a few of his left fingers in a crack.
  
• 26 Enduro Corner 5.12d - [4] Practiced >40 times
• 27 Round table traverse 5.12a [5]

Difficulty Class - Class 5 is technical rock climbing where you need ropes because falls which would kill you are likely. 5.9 was considered the most difficult you could do without aid (where progress is made by climbing directly on equipment placed in or on the rock and not the rock itself). As equipment and climbing technique got better higher sub-classes were added.
5.11-5-12 Expert routes are vertical, and may have overhangs with small holds. Dedicated climbers may reach this level with lots of practice.
5.13-5.15 are for professional climbers.
See Difficulty Class

A Record-Setting Climb Up El Capitan, Without Ropes - The New York Times
Larger route map
Freerider (5.12d) | The Outbound

Other links:
Freerider - American Alpine Club (AAC) Publications
Behind the Scenes of Alex Honnold's Freerider Free Solo - Climbing Magazine
Alex Honnold's Freerider Free Solo: 360 Degree Video - Climbing Magazine
In 'Free Solo,' A Steeper Challenge (moving out of his van and maintaining a long-term relationship.) For Alex Honnold Than El Cap - capradio.org

How Alex Honnold Did It: A Play-By-Play of His Free-Solo Climb on El Capitan - Men's Journal

Honnold Foundation