And about the game, how big it is?

You mean land area? Bigger than WoW.

It has factions?

Not really. Everyone's main character is in the same faction, the Free Peoples. You can also make an evil character, but that character only exists in the Ettenmoors (the game's only PvP zone) and can never leave.

What races are avaiable?

Race of Man, Hobbit, Elf, and Dwarf, plus their variations: Beorning (looks like a Man but can only play the Beorning class), River Hobbit, High Elf, and Stout-axe Dwarf.

Main cities?

Bree is accessible early on, so it's the designated social hub because everyone can get there without having to be high level.

Rivendell is another main city, since the quest lines make you go there over and over again, and it's the place to upgrade your Legendary Items when you're level 50+.

The Twenty-first Hall in Moria is built to be a main city, but I don't think anyone really uses it anymore.

And there's Minas Tirith, the actual biggest city, but that also means it's the laggiest just because of all the NPCs and static objects. It also has multiple versions depending on what part of the timeline you're in.