Terminal application is located on the following path:



Mac is running on UNIX, which is nearly 40 (yes, forty) years old operating system. One of the major advantages and drawbacks of using UNIX is it's command line.
Everything that you know how to do with mouse and windows (clicking, dragging, etc.) can be done and achieved using the command line.
Power of UNIX is the ability to direct input and output of these relatively simple commands and combine them into infinite structures. A bit like bricks and mortar.
Essentially simple, but put together, the only limit is your imagination.
Here are some examples of guides writen for some of my clients.
Network trafficGet a list of of all TCP/IP traffic your computer is currently making.


You will get a screen printout of all current network traffic.
Slow Mac networkDisable writing of status files on the network.


This will stop your Mac from writing previews and caches on remote file systems.
Reset spotlightEvery now and then Spotlight gets corrupt indexes and needs to be updated.
sudo mdutil -E /
Disk usageYou can examine exactly what the system reads and writes to disk.


:
and press 
You can now examine the contents of usage.txt file on your Desktop, and see what the system was doing...
XML tag checkMost software is using XML files to store any application preferences.
XML is very similar to HTML, as it is plain text file, and its structure is based on pairing tags.
Checking the integrity of these tags ensures smooth behaviour of your applications.


If every file in the list is followed by OK, then everything is fine.
If not, check the offending file name in a text editor.
Remote accessBefore doing remote access, configure your router to pass outside traffic to HOST machine on port 5900.
On HOST machine:
On a CLIENT machine download Chicken of the VNC (COTVNC)

And there is the HOST screen. You might have to reduce screen resolution and colour depth depending on your upload speed.
2D DockTo change the Dock in Leopard to 2D appearance
defaults write com.apple.dock no-glass -boolean YES
Lock the DockTo lock the contents of the Dock
defaults write com.apple.dock contents-immutable -bool true

To unlock the Dock use:
defaults write com.apple.dock contents-immutable -bool false

Bonjour ScreenShareTo get a more friendly ScreenShare open dialog box
defaults write com.apple.ScreenSharing ShowBonjourBrowser_Debug Yes
To get more options on the toolbar
defaults write com.apple.ScreenSharing 'NSToolbar Configuration ControlToolbar' -dict-add 'TB Item Identifiers' '(Scale,Control,Share,Curtain,Capture,FullScreen,GetClipboard,SendClipboard,Quality)'
Using any of these commands without appropriate skills can result in ruining your machine!