How much output ?

GREAT! Now I don't understand anything once again . :-[ :-/

So could someone pls explain me the buton example (what's happening exactly) so I as a complete noob understand it ? and than maybe i'll understand the more complicated things as well.
As Lefty said I need to understand the basics first, and it looks like I don't hehe . But Lefty's description was allready pretty good for me to understand. Only thing I didn't get yet is:

When the switch is closed there is a current flow from ground through the resistor to +5vdc and the input pin 'senses' this +5vdc voltage level and creates a HIGH reading

Why is it 5 Volts even if it has a resistor between ? I've connected a Resistor to 5V and than I meassured the Voltage btw the end of the resistor and ground and I didn't get 5V. So why do I get 5Volts in this button example ?

Maybe you could give me the calculation with that ohm law.

Greetings
and thx againg for beeing so firendly to me