RPG Maker XP Beginner's Tutorial
Database - Classes
Each actor in your game is a certain Class. This means what kind of fighting style they use. RPG Maker XP comes with 8 default classes, but you might like to edit them or make your own.
Making a New Class
Start off by choosing the Classes tab in the Database. Change the Maximum from 8 to 9 and you'll have your new, empty Class. Now it needs a name. I think I'll make a Ninja class, so I'll name it "Ninja." Next is the Position. Position decides where your class will stand in a fight. Strong fighters stand in the front, weaker Clerics and Mages cast spells from the back. Ninjas are strong but stealthy, so I think I'll put them in the middle.

Now we set the Equippable Weapons and Armors. This means that your class will only be able to equip these specific weapons and armors. If the preset items don't really match your class, you can make your own. I'll choose the closest things I can find.

Element Efficiency and State Efficiency can make battles a lot more interesting. These determine how well or how poorly an element or a status effect works against your player. The values for Elements go A B C D E and F. A=200%, B=150%, C=100%, D=50%, E=0%, and F=-100%. So if we set Fire to 200%, that would mean that this class would be very weak against fire, and fire attacks would be very efficient from the enemy. If it was set to -100%, your player would actually gain HP. 0% would mean the attack would have no effect.
Ninjas lurk in the shadows, so I will set light to B and Darkness to F.

State Efficiency values go A=100%, B=80%, C=60%, D=40%, E=%20, F=0%. I don't think a ninja can be dazzled, so I'm going to set Dazzle to F. Ninjas aren't safe from poison though, so Venom will be set to B.

You can take more time to customize the efficiency for your classes as you like. Next we'll choose which skills your class will learn and at which levels. Either double click or right click and choose "Edit" on the top of the white box labeled Skills to Learn.

Now decide at what level they will receive this skill, and which skill they will learn! I'm setting Level 1 and Paralyze. You can enter as many skills as you like, and multiple skills for each level. You can also make your own skills if you don't see ones you like.

And that's all there is to it! Go back to the Actors page and make a new actor for your new class!