From the Rulebook:

Classes and Abilities
This portion of the rules covers how classes are typed and explains their written stats. The classes listed below form a simple basis for role-play: it is just as easy to play an Ashigaru, Samurai, or even a Sohei monk. Your character and persona are built upon your actions and role-playing abilities: the classes are mere structures, not some prison designed to make you conform. Play Wandering Ronin within the rules of the classes, but without any boundaries to how you imagine your character should be.

Classes are listed in the following manner:

Name: The name of the class that is being described.
Examples: A brief description of the class with a few historical and/or fantasy references.
Garb Requirement: Specific clothing needed to demonstrate which class you are playing. You are required to dress in garb suitable to your characters period of history in addition to this class specific garb. Failure to do either will result in playing the day as a Peasant or civilian.
Armor: Maximum beginning point value of armor the class may choose to wear. You may wear armor with a point value higher then you are allowed to claim, but in these cases the armor still only gives you the maximum allowed for your current race, class, and level. Example: a 1st level Ashigaru wearing full plate still only gets the protection of a single point...
Shields: Largest size shield available for use to that class at 1st level.
Weapons: Different types of weapons that the class may use at 1st level.
Immunities: What abilities, etc. the class is immune to.
Lives: The number of player lives the class has at the 1st level.
Limitations: Some classes have specific restrictions to balance game play.
Abilities and Traits: Specific extraordinary powers granted to a class for each level of experience gained. They are non-magical in nature and may be used on any other player unless specifically noted.
Credits and Levels:

If you wish to fight or participate in a battlegame, you must conform to one class for each game. Only one attendance credit may be given on a single day, with the exception being Coronations, Mid-reigns, and multi-day events, which award two credits per day. You must play the class you wish to gain credit in for the day. If no class is played (a day of Line Battles and tournaments) but fighting takes place, you may take a combat-class credit. All classes level up and gain new abilities according to the following chart:

1st Level - less than 10 credits of experience in that class
2nd Level - at least 10 and less than 20 credits of experience in that class
3rd Level - at least 20 and less than 30 credits of experience in that class
4th Level - at least 30 and less than 40 credits of experience in that class
5th Level - at least 40 and less than 50 credits of experience in that class
Masterhood- 50 or more credits of experience

All classes are played to add an element of reality and fun to the field. There were very few warriors in Medival times that were proficient in ALL forms of combat, so specialization came about. While there are many classes to play that are listed, you don't necessarily have to play them as the class they are based on. You can dress up as a pirate and claim a Soldier credit as long as you have the right sash and follow the rules for a soldier. Dress up as a full-plate Knight from 1500s-era Germany and take the credit as a Samurai. The rules are for continuity: the role-playing is up to you!