Of course I know that the game is in Tamriel, but what country?

I know that you can visit Cyrodil, but how about the Summserset Isle, Elsweyr, or Valenwood? Or can you travel anywhere on the continent?

All of tamriel.

All lands. But with the exception of Cyrodiil you cannot see everything of the provinces. They are devided in zones and some of it is kept sealed for the use in future expansions and content releases.

Tamriel

Just to be more specific...

From developer comments and other materials released so far, it appears as if the areas playable at launch will be:

• Aldmeri Dominion: All of Valenwood, the easternmost of the Summerset Isles (Auridon, including the cities of Firsthold and Skywatch), and two small pieces of Elsweyr including the area around the city of Dune, and an island off the southern coast.
• Daggerfall Covenant: The areas of High Rock and Hammerfell surrounding the Illiac Bay, plus at least part of the Alik'r Desert (essentially the area covered by the game Daggerfall), and the islands of Stros M'kai and Betnikh.
• Ebonheart Pact: Eastern Skyrim, the western and southern mainland of Morrowind (no Vvardenfell or Telvannis Districts), and a small piece of Black Marsh around the city of Stormhold.
• Cyrodiil (AvAvA area): Central portion centered around the Imperial City, not including the Gold Coast (the areas around Anvil and Kvatch) or the Lower Niben (Leyawiin and Blackwood).

Below level 50 you will be restricted to your own faction area and Cyrodiil. At level 50 you will be able to visit the other faction areas, although there appears to be a quest requirement to do so, and you will not be able to interact with any players from within those factions (it wiil be a separate copy of the area for members of your home faction).

Not totally true--Unless they changed things, you can enter Cyrodiil as early as level 10. The game will scale your level up to 50 so you're not completely helpless against higher level players, but since you won't have the equipment and developed skill lines of an actual high level character, you'll still be at a disadvantage.

?

As I said:

too bad they are not alowing players to set the game ^^

Ah derp. Don't mind me, my brain is busted today.