Terminal for android I'm still learning how to use the terminal. I know the dangers of fiddling with it. But I want to use the terminal emulator app to navigate my phone(messaging, camera, launch applications, etc) from the command line. What are the commands and where should I start
My first suggestion would be to take a Nandroid backup (requires a custom Recovery) first if you've had an unpleasing incident on some other OS, or want to recover from one after fiddling with terminal on Android. 


  I want to use the terminal emulator app to navigate my phone(messaging, camera, launch applications, [and so on).]


Messaging and Camera (UI not HW) are also apps in Android and are accessed in the manner similar to other apps (they have their .apk in /system/app). The most common way to access an app is to call its component or activity using am command. Consider this as an example to use am. See more examples on Stack Overflow like:


How to start an Android application from the command line?
How to run a specific Android app using Terminal?
How to start an application using android ADB tools?


am will only launch a part of the app and possibly would need root access if called without ADB(has higher privilege then a normal user). So how would you interact with the app from command line? 

For that, I prefer to use Android keyevent or Pointer location (under Developer options) combined with the input command.  See:


ADB Shell Input Events
How to use ADB to send touch events to device using sendevent command?


You would now be able to launch an app with UI and can use the app rather easily from command-line. 


  What are the commands?


I'm not aware of all the commands but you can take a look at /system/bin and /systen/xbin (like /bin and /sbin in GNU/Linux). You'll need root access to use some of them. (See Busybox too.)


  Where should I start?


Well, I'm unaware of a crash-course and I would advise to work on an issue or a possibility to learn the know-how of terminal rather easily. Try this answer for a start.

Good Luck!