Are Dothraki and High Valyrian the same languages?
If not then can u explain me who uses each one?
No, they are not. If you've watched the show, you know who the Dothraki are, and they are obviously the ones who use that language.
High Valyrian, on the other hand, is a dead language by the time the events of the show happen. Valyria was a country in the south of Essos that was destroyed in a catastrophic event 400 years prior (called the Doom). Before that, the Valyrians had colonized pretty much all of western Essos, as well as Slaver's Bay, which is why the people there speak an assortment of related languages (Bastard Valyrian). The Valyrians were the only people who could ride dragons, and the Targaryens are the last noble Valyrian family that survived the Doom.
Just to add to that: it seems from material in the books that highborn children are often taught High Valyrian by the maesters who serve at their castles. Tyrion, Arya, Ser Barristan, Samwell Tarly, and Quentyn Martell are all mentioned in the books to have some familiarity with High Valyrian.