IT

A good online manual:

Command-line reference A-Z

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Some notes:

To display help information for a command, just type the command name followed by "/?".
Example:

C:\>xcopy /?

Redirect information from the screen to txt files:
Example:
C:\>dir >myfile.txt
C:\>tree >myfile.txt
(you can edit the txt files with: C:\>edit myfile.txt)

Dir

Display one page at a time:
C:\> dir /p
C:\> dir | more

Xcopy

copy all new data (files and folders) from source to destination:

C:\>xcopy source destination /D /E /C /R /H /I /K /Y

tasklist and taskkill

tasklist: displays a list of applications and services with their Process ID (PID) for all tasks running on either a local or a remote computer.
taskkill: ends one or more tasks or processes. Processes can be killed by process ID or image name.