Hello everyone i would want to know how to main a champion , and how to chose the champion ive watched many videos , and they all say its about your play style. I'm not sure to know what they mean , I like to play a strong Ap / Tanky Champion. Is that what they mean ? Please help thank you , and have a good day
From the way I've always understood it, Maining a champion means playing them religiously. Learning the ins and outs, learning what champions counter yours, learning which champs you can do well against, learning how to properly itemize against said champions.
So far as picking a champ, that's a little harder. Do research, play as many FTP champs as possible, and try a variety of roles (if possible).
But disregarded all of that even, just find a champ that sounds fun to play, that's how I found my main. 
Love his kit and how if played properly can melt pretty much any one champ.
as far as i know on the picking part what i would do is find some champs that you think would be fun to play usually about 4 or 5 and then just going through the list and try and find one you enjoy if you dont enjoy any of them go back to looking and choosing champs for the list until you find a champ that you enjoy enough to take the time to get good at
"Main" just means that they, in their estimation, play the champion often.
"how to chose the champion... they all say its about your play style."
That just means "who do you like to play and what are you good at", and the "what" can be changed by often you chose the "who". So yes, AP/Tanks like Vlad.
Also, quick tip for 
. It's a pretty obvious one, but some people try it as the answer may be obscured by the math. Don't try to build tank to get AP for Vlad, it doesn't work; one still only builds defensive items as appropriate. Build as normal and enjoy the bonus tankyness from the AP instead.
Sounds like Cho gath would be a good pick for you. He always gets a certain degree of tankyness if you can keep your ult stacked, and besides that has a fairly versatile build where you can change the amount of tankyness you build for each given scenario.
Maokai is also a decent option, although he focuses more on the tanky part than on the Ap part.
If jungling is what you like then check out sejuani and amumu who are both very strong right now.
Vlad is not super tanky, but he is definitely far from squishy especially if you get fed.
For any of these champs just play a few games and decide if you like them. Pick your favorites and focus on getting really good with them.
You don't NEED a main, you can also have a small pool of champions that you love to pick. A healthy amount would be under 18. Like 3-5 for the lane/area you main, and 2 minimum per lane you don't main. Like this, you can fill and cover all areas of the map. This doesn't prevent you from playing your favorite mid laner 95% of the time, just make sure you have your champion pool.
By playstyle they mean exactly that. Do you prefer marksman, support, DPS bruisers, tanky bruisers, tanks, assassin. Do you prefer staying from a distance and dealing damage or be close up in a fight and deal lots of damage. Do you rather take risks (assassins or alike) or play safer. Are you a fan of teamfights (AOE damage abilities) or more of a 1 vs 1 person. Do you rather play a melee champion, or a ranged champ.
etc etc.
On a side note, I played quite a bit of Vlad myself. The more mobility and raw damage, the better it is. I have a particular rune page for him: http://na.op.gg/summoner/rune/userName=wow%20cc%20nub (look at #10 Vlad). 5% in my runes and going 21/9/0 masteries allow me to get 10% CDR at lv 1. Getting Revolver + boots of lucidity gives me sustain and lots of cooldown for my Q. Then I rush a Zhonias and raw damage items. (the closest thing to tanky items should be zhonias/abyssal).
Vlad is rad. The thing with him is if you arent good with position/ map awareness, he isnt a good choice. The meta is all about mobility right now. So you either need to be godlike with a non mobi champ like Vlad, swain, singed, maokai. Or you need to work on your mobile champs more. I've mained Zed for most of my playing time (beginning of season 3) because he is the most fun for me. Find a champ that you don't bore of and play him to death. Then you can beat "counters" and play well in your games. But the thing about "Mains" is this. It doesn't mean you have to exclusively play that champ. You don't need to be "Irelia carries U" you can play other champs. It's just that when you play your main, you feel more confident in the game cause you are experienced with said champ. Hope this helps and good luck!
Be one with your main.
is a playstyle.
Keep playing as many champions as you can. If you haven't found something that clicks with you, the next thing to answer is why? What is that champion missing? That should at least tell you what champions you should look at next. The idea with playstyle isn't just necessarily the build, but what you want the champion to do. I want to get in there, be scary, and wear everyone down as noone can kill me (Vlad/Lissandra) is different from "I want to pick my fights but be really tough" (Rumble/Diana), which is also different from "Nobody can move unless I let them" (Cho'gath/Maokai), although all three of these groups are Tanky/AP.
When you get to a style described like the above, then you can get to other champions that aren't necessarily AP/Tanky, but do what you want.
Some AP/Tanky champions to look at might be Rumble, Maokai, and Lissandra (people have already mentioned Cho'gath and Vlad).
