When I saw this guide it felt like a kick in the balls.

You could play Janna as Ad Carry.
But for this you have to build at least an Infinity Edge and Bloodthirster additional to the Attack speed items.
I don´t advise playing her on As, but if you do so you should use more on Hit effect items like Malady instead of Phantom Dancer

I guess jana supposed to be support then dmg dealer

This build is silly, and I mean REALLY EFFING SILLY.

First of all, you went for Nashor's Tooth on an AD guide. *Facedesk*
Second, Zeke's Herald even though you got absolutely no damage prior to this. *Facedesk*
Third, you got Phantom Dancer, yet again with no damage prior, and no Infinity Edge or any other crit item for that matter to synergize with it. *Facedesk*
Fourth, Madred's Bloodrazor, decent choice on any AD Champion, BUT IT'S THE ONLY ITEM THAT GIVES AD THAT YOU BUY....... *Facedesks twice*
Fifth, Ionic Spark, with this item you broke the attack speed cap.

Now lets look at your Janna. A support champion with all AP scaling skills, that has all the attack speed in the world, 132 damage + 50 from Eye of the Storm, only 182 damage -.- , some on-hit effects, yet you have life steal which will be doing nothing, very squishy, a little bit of crit for no apparent reason, high movement speed, and a tiny amount of AP. *Facedesks until unconciousness, then wakes up and facedesks again*

Hate to break it to you this way, but THIS BUILD SUCKS.

Lastly, the build is a wall of text with one video that DOESN'T EVEN SHOW AD Janna.

Here's a guide to help you with that:
Making A Guide
Please read the whole thing.

I think my work is done here.