Hi, i play vel'koz 
a lot and i think im really op with playing vel but i have no idea how i can win from champions like zed
, talon
and yasuo 
becuase they are allmost impossible to hit with an abilty and they burst me down in 5 secconds.
Being AD assassins they basically counter immobile long ranged casters in lane. So first of all I would probably avoid those matchups.
I know you can't always do that. But if you get such a matchup it is highly in their favour to begin with. I haven't got much experience on Vel'Koz myself but this looks like a classic Morello+Zhonja core build will be the go-to build here. Zhonja's is your bread-and-butter anyway or you won't survive on fights. Make sure to use that active to its full extent. Consider tanky items: not RoA but Rylai's, GA, Guise..
Fearing an Ignite on their side, I would go for a defensive pick, neither Ignite nor Heal (Ignite will half a Heal and those guys beat you in terms of sticking power even with a 1 sec MS boost). Barrier is your friend against most assassins. Especially against Zed, Exhaust can be worth even much more, (just drop it after his ult animation and it will deny tons of damage).
As such assassins are melee type, you can usually bully them early, (even if it's only pre3, depending on the matchup). A Talon cannot jump on you on level 1, a Fizz won't want to trade with you... If they transition to the point they can attempt to shut you down when they're already at low health, this'll help a lot. Goes without saying you can possibly establish a little gold lead before they get dangerous and be ahead in items after the first backport. No point in hiding from the start.
If you haven't figured that one out yourself yet: while Yasuo can block some spells of yours, your ultimate is not a projectile as far as I'm aware.
Talon is a bit of a "stepping" practice, to my mind. You need to know his exact E range (the jump) and stay out of it at all times, basically. That's the only way he can really get you. Myself, I've grown into loving Talon matchups with ranged casters, they're quite fun. Do not let this guy get ahead in MoveSpeed too much so you can avoid him. On some champs like Ori I tend to even bring MS Quints on Talon matchups.
And two more general ideas against assassins:
Oh i just play 
and eat and alive. Never played him vs a though
I haven't got much experience on Vel'Koz myself but this looks like a classic Morello+Zhonja core build will be the go-to build here.
Naw, Vel'koz has bad AP ratios, especially on his ultimate. He works better with MR reduction. Its because he doesn't need large expensive AP items to get work done that he's viable as a support. He's also quite good at kiting. He has above average MS, can cast while moving, and his basic combos start with a slow/knockup. Backing away while firing is how he deals with attackers. But OP, you have to hit. With aggressive melees, try dropping an e->w at your feet when they jump on you, or q-w if they're chasing you. For hitting them when they're farming, you do it when they go to last hit.
5 secconds.
Thats pretty slow man...
For all of them, rush Zhonyas. Or at least Seekers.
Save your E for when they use their mobility skills. When Talon jumps you cast your E under you, same with Zed ult.
just plain hard counters you. Shield vs an almost fully projectile based kit (even his W, so I've heard) and so much mobility you can't land anything. Just farm as much as you can, shove so he can't shove you in, and wait for late game. Maybe roam.
Rush seekers into morellos and then go a standard penetration build.
FYI, you are supposed to lose to those 3 champs
You don't have to take Ignite every time. Depending on the other champ, exhaust may be a much better option. Zhonya's + Exh and you should be fine
