Eversmile is the name of the level in the Dungeon Keeper Demo. It demonstrates some of the full game's themes and devices such as the Hand of Evil, building rooms, and training creatures.
Simply obey the in-game messages. You will need to build a Treasure Room, dig to and claim the Portal, build a Lair, Hatchery, and Training Room, mine some gold, and tunnel to the abandoned dungeon to the north. At some point, some heroes will try to break into your Dungeon, but they are easily dispatched. There, some rooms and a neutral Bile Demon and Troll can be found. You will also find the Speed Monster spell. There are also a few traps, so be careful.
You will then be instructed to assault the hero fortress, and will be given a Bridge to make your way across the lava. After defeating the Archers, you will come across the Heal Spell, some more heroes, and the door to the main fortress. The Lord of The Land will come as you approach it. Kill him and the level is won. There is also a Hero Dungeon Heart, but destroying it is not required.