After the scenes, just follow your team mates to receive your mission briefing. After learning your objectives, head out. Follow your squad as you enter through the buildings. You'll finally reach the street. Stay put and wait for the technical to pass. Cross the street and stack up with your team mate by the door. Attempt to head out and your team will be ambushed. Drag your wounded team mate and keep pressing A to avoid getting damaged.
Once done, help your team take out the enemies outside. Don't worry about your grenades and ammo since there is an ammo crate nearby that can instantly resupply you. Keep clearing the enemies outside, including the two RPG troopers in the building to the south (look in your compass). Take note that your weapon can destroy the concrete walls so use that to kill the RPG soldiers without too much hassle.
After clearing the area, regroup with your team mates inside the building. Follow them to the upper floors until you reach a large room. Sprint past the windows and kill the enemies that will appear from the corner. Continue following your squad to the rooftops.
Don't go ahead since there's a sniper taking potshots at you. Crouch and follow your team mates as you move from cover to cover. Join your team as they position themselves near the cover. Stay put until all of them positions themselves near the edge. Crawl towards them and grab the AT they'll hand to you. Press X to equip it and WAIT for them provide suppressing fire. The target will be marked in the hotel; just aim your weapons and release your projectile to destroy it.
Next, head to the corner of the rooftop and cover your allies below as they extract your wounded comrade. Take out any hostiles who will appear from the alleys and the buildings. Continue helping them fend off three waves of hostiles until they get to safety. You will also unlock an achievement here if you killed most of the enemies, including some runners who will attempt to rush towards the building you're in after Doc Holiday leaves the scene.
Not on my watch!
Next follow your team mates as you cross the other building and descend to ground level. Continue to the next building where you'll find another ammo cache. Resupply and continue clearing the building. Head outside to find a destroyed HUMVEE and stay put until your orders are given. Trace the wire as instructed and it will lead you to a set of devices in a basement. Interact with it and beat up the terrorist who will attack you.
Return to the street and head to the overpass to get the LMG. Use it to fend off the enemy attack. After successfully defending your position, get down and head to the next marker. Get up the abandoned technical and use the mounted machine gun to lay waste on the enemies. Take note that you can shoot the cars to detonate them to your advantage. Continue doing this until a catastrophic earthquake takes place. Mission complete.