Companions can be hired and incorporated into the player's warband usually if some requirements are met: some of them will ask for a little money to pay their expenses or old debts before leaving town, while others may demand nothing.
To put it simple, the player is not the only hero(ine), adventurer or wanderlusty mercenary who roams Europe. Companions in Europe 1200 are a special kind of characters the player may sometimes encounter in taverns during his/her travels.
