There are four types of classes: Warriors, Wizards, Priests and Rogues.
Warriors have the Fighters, Paladins and Rangers. Warriors are largely front-line damage dealers or tanks. They get the most HP of any other classes.
Fighters are the simplest of the three, and are essentially just weapon masters. Soldiers, sellswords, knights, etc. Fighters have no magical powers or special skills beyond being really good at fighting. Their ability to hit targets and deal damage is high and gets higher as they level up. They also get the ability to 'specialize' in one weapon. When using that weapon, they get a +1 to hit and a +2 to damage, making them even more effective.
Paladins are holy warriors, champions chosen by a deity to do their work on earth. They get a number of special abilities including the power to heal at a touch (Lay on Hands), the ability to eventually cast divine spells, immunity to all diseases, etc., etc. The downside is that Paladins have a very strict code of conduct that they must always adhere to. Breaking that code, even marginally, causes them to 'fall from grace' which means they lose all of their powers and advantages.
Rangers are loners who live out in the wild and have a deep respect for nature. They gain the ability to dual-wield without penalty, get a number of nature-based proficiencies for free (tracking, etc.), and eventually gain the ability to cast druidic spells.
Wizards are rather versatile. They tend to be very weak (low HP, awful defense), but they make up for it with the ability to cast arcane spells. Wizards begin the game as the weakest class, but eventually they surpass all other classes in power--but that takes a long time and a lot of levels at sucking first.
Most wizards are Mages, which is a standard, general spellcasting class. However, there are also specialists who specialize in a particular school of magic, like Necromancers, Summoners, or Enchanters. Specializing in a school of magic means your spells from that school are more potent and you get more of them; downside is, you can't access certain other schools as a tradeoff. However, general Mages can access any school they want.
Priests are servants of the gods. You can read up on the different religions in the Lost Souls Handbook thread. By dedicating yourself to a specific god, you gain certain powers, including the ability to cast divine spells. Other powers depend on the deity you are serving.
Clerics are your standard priest. There are also Druids, who serve nature instead of a specific god. Their spells and abilities are somewhat different, but the basic idea between them is the same. While wizards study books to earn their spells, priests get their spells and powers from their god directly. Of course, that means if you piss off your god in some way, you lose your powers.
Rogues are an unusual class. They come with a large number of special abilities that aren't always helpful in the battlefield, but are immeasurably useful in other situations. There are two types of Rogues--Thieves and Bards.
Thieves have lots of special skills that they can use including picking pockets, disarming traps, picking locks, and stealth. They also get the ability to 'backstab' which is an ability you can use to do extra damage to an opponent if you can successfully sneak up on them from behind.
Bards are entertainers; singers, players of instruments, poets, actors and so forth. They have some of the same skills as thieves, and can cast arcane spells like a mage, but they also get some unique abilities, too, including an empowering song that boosts your allies fighting ability. Bards are kind of 'jack-of-all-trade' sorts. They aren't better at fighting than fighters, better at magic than mages or better at thieving than thieves, but they can do just about everything a little well.
Kits are a class modification that a person can take. You apply a kit to your class, and it changes some of your abilities in some way. Usually it's a trade-off of some kind. For instance, if you are playing a thief, you might take the Assassin kit. You'll lose some of your thief-related abilities, but in return you'll get other abilities that relate to being an assassin, like the ability to use poisons or make a special 'deathblow' that does extra damage if you catch your target unawares.
There are lots of kits; too many for me to list them all. Plus, I can make new kits, if you have a character concept that needs one. A few examples of some kits that might be useful to this particular campaign, though? Let's see...Mariner (fighter who prefers naval weapons like cutlasses and sabres and doesn't wear armor, but gets some special sailor-like abilities to make up for it), Fathomer (a mage who specializes in deep sea diving and so has spells and abilities that lets you survive underwater), Swashbuckler (a thief who gets some flashy moves and a slightly better fighting ability in exchange for some thief skills) and so on.
Statuses are just something I came up with that tells the current status of a character. It's to help remind them of certain things to help gameplay be more realistic. Like, if you haven't bathed in a week, you'll get the 'Ripe' status which is just a reminder that hey, you are kind of stinky right now. And NPCs will react accordingly. Or if you've been out in the rain for awhile, you'll get the 'Soaked' status. Mostly, it's just to help remind me and the players the current condition of their characters.