You've woken up in the Animus but they've put in an Operating System update since you've last used it. Rebecca is going to have you run through a couple simple tasks to make sure that the OS update went smoothly and to get you reacquainted with the system.
When you've rematerialized with some actual terrain in front of you, you'll be given your first objective. Rebecca will mark an area ahead with a green marker and you need to get to it. Just run forward using the button as prompted. When you approach the wall, keep holding that button and push towards the wall to run up the wall.
Once you reach the marker, it will move again but this time you will have to climb. Climbing is pretty similar to running up walls. In this case, approach the wall and run up to grab onto the handholds. You'll start climbing in whichever direction you push. You can go up, down and sideways as is necessary. You'll have to look for handholds which can generally be anything, even including decorative moldings.
Keep climbing up the wall and when you can't climb up any more, push to the left to go around the corner. Keep climbing up and then left until you get to the next marker.
This next section may be a little more difficult because of the white on white colors here but you need to run across the various beams in front of you. This is very similar to just running. If you see something nearby that you'd like to jump to, simply press the run button and push towards that platform. You will never simply run off of an edge but if you would like to jump off of something where you wouldn't normally be able to run, hitting the jump button will accomplish that.
At the end of your course, you'll climb another wall and be told about what a "constraint" is. These are essentially optional objectives that don't need to be completed but doing so will increase your synchronization. They can vary from making certain kinds of kills to simply completing a feat in an allotted time. In this case, you simply have to perform an Air Assassination. Walk onto the plank and when you get to the end, hit the attack button to jump off the beam and kill him. Similarly, walk ahead a couple of steps until you are looking over the next enemy and then attack again to kill him as well.
After you've killed them both, continue forward, jump into the gap and then follow the rest of the obstacle course as it leads you along to windows and buildings. As you run along the area ahead, it will start to take shape in front of you.
