Sequence 01, Memory 02 -- A Narrow Escape
In this menu you also have access to the DNA Menu, the Map, your Inventory, and the Database. Now would be a good time to look at the Database as it only has two entries -- the Bomb Codex and User Manual.
The Bomb Codex shows you the entries for the Impact Shell, Fuse Shell, Trip Wire, Sticky Pouch, Datura Bomb, Smoke Screen, Cherry Bomb, Thunder Bomb, Splinter Bomb, Smoke Decoy, Caltrop Bomb, Gold Bomb, Blood Bomb, and Stink Bomb.
The User Manual has a large number of entries -- and I recommend that you read at a minimum the Story Entry, the Controls Entry (because they have changed since the previous games), and anything that you are not familiar with. The Den, Bomb, Desmond's Journey and Mediterranean Defense Entries are obvious choices...
When you are done go back to the game world and follow the ghost of Ezio on the route that you actually took in the first game -- take out the one guard and you will zone inside at the top, check out your unbroken Hidden Blade, and obtain a sword before following the ghost through the nearby door and up the stairs. At the top you will battle four guards -- be sure to loot them by holding the 'B' Button while standing near their bodies as they will have very useful stuff!
Continue to follow the ghost now, and you will climb the Keep -- last time we did this it was a Summer evening if I recall correctly -- and eventually you will reach a ledge with a guard above and use 'X' to do a ledge kill. After you loot the body keep following the ghost and you will take out another guard and learn the swinging move.
A Counter-Kill for Full Synchronization
Note that when you reach the roof here you may experience a nasty element of the controls in this game -- if you have played the previous games you will remember this and not fondly -- as the game will sometimes have your character do things that get it hurt when you did not tell the controller to do that. Sigh. I really wish that they had fixed this, but no, that same damn shoddy control system is present in yet another game in the series...
If the game insists on having your character jump to the left when you climb onto the roof no matter how much you do not tell the controls to do that, and you fall over and over, the solution to this is to hang from the edge of the roof and shimmy all the way to the right and THEN climb up -- you will not be forced to jump to the left if you do that.
Follow the ghost to the Eagle Statue and hit 'B' to interact with it, pushing it off the edge to break through the ice below, allowing you to dive into the water.
-- Synchronization Point --
To complete 100% synchronization you need to do a counter-kill on one of the Templar -- it does not have to be the last one after you jump off the roof into the water -- in face I recommend you do it on one of the four you battle after getting your weapons back...
To do the Counter-kill hold the Right Trigger to go defensive and, as he attacks hit the 'X' Button to execute a Counter-kill. If your timing is good, voila! Full Synchronization! If not, well, climbing practice it is, mates! If you have trouble with the timing for doing a counter-kill or this is new to you it really is a good idea to do it on the fight with the four guards just after you get your weapons as that gives you more opportunity to learn the move.
After you kill the guard in the passage you need to check the map to find the next memory synchronization point -- and then head there to trigger the next memory!