Houses are the buildings were most people live. Many come in different shapes and sizes. However, there are some you won't be able to get into that easily. Such Houses feature 'locks', with a certain level, indicating how difficult it is to break into the house.
As always, Going into Houses and buildings in general wil provide you with more ( if only a little) information on the ever-changing world of Ersarn. In addition, this is an oppurtunity to aqquire more quests and the like. some of these won't be found easily buy going to a guild.