controlling the mouse programatically.

[C# Programming]

hello,
please help me,

actually I have 3 questions:

1. how can I know programatically when a click has occured on the desktop? (or another application, other than mine).

2. how can I perform a click or move the mouse programatically or perform keyboard clicks etc.

3. how do programs like team viewer send the image of the desktop so efficiently?
I know they somehow capture only the changes in the client's screen. do they read the changes made in every pixel and send only those?
or is there something else?

if this is the case, how can I read the information in each pixel on the screen?

Thanks alot in advanced!

-Ben