how do i stealth assassinate someone? everytime i try assassinating a target he discovers me, is there away for im not to notice me and me to assassinate him and the guards dont know and i just walk away unnoticed?

All you have to do is selecting the hidden blade.
Lock on to a target.
And when you're close to your target, press Square.
Don't Hold R1 while pressing Square, that will draw attention immediately, all you have to do is press square, and nothing else for a stealth kill.

Unless you're talking about one of the 9 men you need to assassinate, then that's a bit tricky, because you need to approach some of them in some different ways, and attack when you think will be the right moment to attack.
And even if you try a stealth kill on one of the 9 men, then you still gets guard after you if they see you, or are close by during the incident.

And if there are a few men there in a group, don't forget to use your throwing knives. If you sit on a rooftop and kill one, sometimes the others won't see you aand you can knock em down one by one

if you're talking main targets, its really, really, really, REALLY hard to stealth assassinate them, but it is possible.

yh like the ones above me do not press R1 and for throwing knives as soon as you hit break any line of sigh so go to the middle of the building your on ive been caught a couple of times like that

personally i think throwing knives make the game too easy any1 agree??

Not really cause u only get so many and if u r out u need to pickpocket a thug without him noticeing but thats not to hard.