These are the second, third and fourth missions of the game.
On Siena, you have to move across roof tops and then at the end you will get into a button mashing mini-game. Use a lot of cover as you move across the rooftops.
On Opera House, remember to move very stealthy as it is much easier. You have to avoid some cameras on this mission and avoid enemies and then at the end, you will have to snipe enemies.
On Sink Hole, make sure you use a lot of cover to avoid helicopter gunfire. Move slowly and wait until the helicopter gunner stops shooting before moving to the next cover. When you reach the downed helicopter, use the turret until your screen turns gray and then run behind the helicopter for cover.