Telehack has a bit of a learning curve, but don't worry. That's how all computer systems were back in the day. Most of the fun comes from exploring and trying to figure things out on your own. If you want to maximize your experience, read very little from this Wiki, and only use it when you're 100% sure you're stuck. Telehack itself contains tons of hints, and even though it doesn't seem like you have enough to get started, you actually do. Just keep looking and experimenting.
When you first go to telehack.com from a browser, you will notice a list of commands and a prompt to type at. You are at the command prompt on the Telehack server, your home server. But you aren't logged in yet. You can type these commands and see what they do to learn more about them. You can also type "dir" or "ls" to see a list of files located on the server. To read the files, just type "more <filename>" or "type <filename>". You can find lots of help and/or entertainment in these files.
If you log in, you will have access to even more commands. The first time you log in, you will be creating a new account, so choose your username and password carefully. You will be typing that username and password many times, so pick something secure, but something you can type quickly but also something that won't be easy to guess (i.e. 12345).
Telehack uses many of the old commands and conventions (though most of these have been simplified). "Help" and "?" were the way to answer questions back then, and they still are. These commands can be used at almost any prompt. "Quit" and "Exit" will close most things, but if you're stuck, Ctrl-C is the ultimate way out.
You can get more help from the online users using "Relay". This is a chat system that lets you chat in real-time with currently-logged in users. If you're looking for an authentic experience, use relay to get help before consulting this wiki. ;)