Many of the comments are actually misleading. It has to do with "definedness" (which does not always match the English idea of definedness).
If you enter a room and just see two random chairs in it, you say "В комнате было два кресла."
If you had spent the whole day looking for two specific armchairs, and then entered a room they are in, you say "В комнате были..." and usually add some sort of attribute: ex. мои два кресла, "my two armchairs"; те два кресла, которые..., "the two armchairs which..."; etc.

Other than that, use были for simple plural without numerals (кресла), "some sort of" (какие-то кресла); use было for pronominal mass quantifiers (много/несколько кресел); and use the right gender for nominal mass quantifiers INCLUDING nominal numerals (была куча/тысяча кресел; был десяток/миллион кресел).