Chapter 4 is a shorter chapter than most, but with The Trial of the Titan and The Archaean to deal with it's not short on action. Complete Chapter 3, then begin with the A Dubious Drive step to get this underway.
A Dubious Drive
There's not much to do here beyond following the car.
Onward to the Disc
Talk to Ardyn and then follow his car again.
Disc of Cauthess and The Archaean
Drive along the dirt road until you reach a dead end, then hop out and move to the marker on foot. Grab the sword, and get ready to hammer Circle / B when prompted.
Follow the path avoiding the flames as much as you can, deal with the Dynoaevises on the way - daggers, guns, and fire are particularly effective here - then when you reach the edge shimmy along the narrow ledge.
Keep heading along the path the other side, and when Gladio confronts you say Yes to gain a 50% strength boost, and at the end of the path you'll face off a handful of soldiers.
The Trial of Titan boss battle
The Titan will throw you around a bit and then you'll be prompted to flee. Follow Gladio up the path dodging the Titan's attacks, drop down into the lower area, and climb up the other side. Run towards the camera and prepare for some QTE-style fighting.
Need more help? Our Final Fantasy 15 guide and walkthrough can provide tips on main story, as well as the open-world's many quests and activities. Learning how to get AP fast, EXP fast and money or Gil fast will aid you in many optional dungeons and tombs - including how to open and explore their locked doors. There's also plenty of interesting side-quests, too, such as the Scraps of Mystery and Professors Protege frog locations. And if you want to get around easier, you can rent a Chocobo, learn the infinite sprint trick and later in the game, get the flying car Regalia Type F. There's also more to see and do with DLC, such as Episode Gladiolus and Episode Prompto.
Block, counter, and parry when prompted, and the rest of the time try and get in a few hits whilst avoiding taking too much damage. After a few rounds of this you'll be prompted to do 8,5000 points of damage before the timer runs out, so run in and let rip with your most powerful attacks to end the fight.
Once done, get ready for the lengthier Chapter 5 where you'll visit new locales and a couple of dungeons.