Dragon Quest Monsters revolves around the Quest system. The Quest system consists of surviving thru several levels of various terrain, many of which have been seen in previous installments of the Dragon Quest series. The terrain is randomly generated each time, so entering the same quest several times will yield different ones. Each terrain consists of monsters, scattered items and a warpgate which allows you entry to the next floor of the quest. When you progress further and further in these quests, the levels you must endure are increased before you confront the final boss of that particular quest.
When going on quests, you might drop to a level where you meet either a special character inhabiting only one floor which makes things easier:
The Bishop: who will heal you completely and enable you to save in the middle of a quest.
The Merchant: who will sell you items if you are in need of any and enable you to save in the middle of a quest.
Treasure Chests: full of good basic items such as healing herbs, anti-poison herbs, wing of the wyvern, etc.
On occasion, you may encounter some people walking the land, be careful because before they will give you any help, you have to pass their tests which is a battle with some extremely strong enemies:
The Bishop: he will completely heal you after you successfully defeat the monsters.
The Warrior: he will give you an item (although I am not sure..but it could be seeds which raise a particular stat..more info on this in the future) after you successfully defeat the monsters.
The Old Man: ??????
Treasure Chests: some which yield valuable items or may be man-eating chests (I have yet to encounter, but I am sure there are some)
Extracted from FAQ compiled by Sugoi