This is a game that you really need to get into to fully enjoy. It is very in depth and can be complicated for first time players.
Your mission is to destroy Lord Chaos. You can find the full story in the link above on pages I-XVIII. At the start of the game, you are walking around a dungeon. Keep going until you come to the " HALL OF CHAMPIONS". Here you get to choose four champions, or characters, to take with you. You have to give them water, food, and sleep. Now make your way through this area and come to a door. Past this door is the "real" dungeon, where the game takes place. Here, you do things such as fight monsters and explore rooms.
In the top right corner, there are four little figures. These represent your characters. The two at the top are in the lead of the party. They will be able to reach enemies with close range attacks so they will usually end up with more experience, especially in the start. Make sure to switch these around so all four get some close range fighting experience. You can still do long range attacks from the back row and gain experience from it.
There is a lot more to this game that I can't explain because I haven't myself beaten or gotten too far in it. I recommend patience and the guide from the link above to those trying to beat. There is a walkthrough and level maps at that link as well as a manual that should explain a lot.
When you load the game, it will ask you three setup questions. Choose VGA for the first and Mouse for the third. Choosing to use the mouse will let you use both the mouse and keyboard. Click on things such as the champions to see/choose them at the start and open their inventories, choose attacks, pick up items, and select options. Right clicking will toggle between a champions inventory (depending on which one you right click on, or the last one you opened if you click elsewhere) and the dungeon view. On the NumPad, the numbers 1-6 correspond to the movement buttons on the bottom right of the screen and Esc freezes the game.