unet and automatic matchmaking.

hi . i am new to unity networking and i started with unet to learn . What is a best way to perform following condition for an online game? players in my game click on battle button and then an algoritm picks tow players and makes a match for them . players will not see any game (room) list and all process must be automatic . how it should be develope ? i think i must have a server that just manage all algoritms and network match making. but what is the limitation for this purpose ? is there unet limitation or server hardware limit for too much player ? is there any useful tutarial or guide to develope such things?