To open up a command line either do Start -> Run... -> "cmd" or do Ctrl-Alt-Delete -> File -> New Task -> "cmd".
The command line (emulated DOS on 2000/XP) allows basic access to the file system, and, more importantly, allows you to call programs with more parameters than explorer. First we need to know how to do a few things:
Change Current Hard Drive
For whatever reason changing which hard drive you are on is different from navigating folders.
All you do is write the drive's letter followed by a colon.
Change current directory
The change directory command is abbreviated "cd"
To go up the directory tree you use '..\' as a folder name.
You can use all of these in combo:
Run a program
You can run a program by typing its name. However, in the case of just typing the name, it must be in the current directory or in the system path. Othewise you must type a full or local path. A local path is referred to relative of the current path. A full path includes a drive name.
Seu nome? botty
In this example I am running a program, booi, which is in the system path. Because I am in the examples folder I may simply give it a name with no path.
There's not much more you need to know, except command line arguments.
Of course, the command line allows you to do much more than just this. Google "DOS command line tutorial", or for a quick look at all the things you can do, type "help".