Here we will look into the questions "What are Chat commands?" "How do i use them?" "Why you should know them?" and "Which are there?" to make it really short.
What are Chat commands?Edit
Coming from the general idea with computers of having a "command line" (text entered by humans to tell computers something), chat commands allow the player to request information or functions from the server by typing commands in the chat window.
How do i use them?Edit
If "using Chat Window to type a command" doesn't make sense to you. The following description should clear this up.
Default Key to chat in Minecraft is the letter 'T' on your keyboard. This can be changed under 'Esc' (on your keyboard again) > Options > Controls. This guide recommends changing it to 'Enter', as most games and many programs with chat/writing function use it and it's very convenient.
By typing 'T' (default) now while ingame on the server (after connecting and the world is displayed) a small window will open on your screen which let's you enter text and symbols. Using the default key 'ENTER' would take whatever text/symbols you wrote and send them to the server. Depending what you write it either is displayed to local/world chat (and therefore to all players currently online) or hidden from them while returning info, function, confirmation and/or error message from the server.
Now when using chat commands all you have to look for is the symbol which is used to type them and write this always before your command to make them work (otherwise it is displayed to some/all players instead, unless that is part of the command). The symbol in this case (for our server) is slash (/). By typing /Help Subjects (case-sensitive, unless all "typos" were all entered on server side by administrator/s) for example, you get a sometimes old list (due to frequent updates) of currently available chat commands.
That's it, you just learned something new, congratulation!
Why you should know them?Edit
While this server differs strongly from official (unmodded) Minecraft. In this still early state of the server, there is a huge dependency upon chat commands, since they simply are the easiest way for both adminstrator (e.g. server owner) to add and similar easy to use for players. There are just a few problems with this explained below. An alternative to using a few chat commands is made by having the custom client Spout.
First: A player can only know a chat command when he somehow got hold of them. This can happen through many ways: from other players ingame, through forum, this wikia or even on this page (if you look further down) or also from the server itself (/Help Subjects was mentioned in the earlier questions answer). Therefore we have the problem of knowledge: you can't use something that isn't known to you.
Second: Most players get tired of them at some point. Including the first writer of this wikia page. If you always have to use /login PW each time the server crashed, your client was rejected for some reason or simply by going off for a moment and coming back. This always can lead to getting a bad mood. To conclude we call this problem acceptance: the will to accept a situation simply how it is.
Which are there?Edit
Many. So many that we need a wikia to explain all of them. Well at least if you call "chat commands" a feature of it's own and call the purpose of this wikia to explain the features of our server. But enough chitty chatty. Here is the chat command list you seeked all way of coming to this page.
Note that chat commands are made in a few minutes and usually take minutes/hours/days to be made public. Never except to see a list of every single chat command there is, it's simply impossible unless written by the alanine himself.
Here you find the actual: Chat Command List.