Help me understand WiFi

I am a student doing a research paper. I chose to do WiFi, because it interests me. Can you please help me understand more about it? There are 3 key questions…
1. What is WiFi and what does it do?
2. What kind of technology is necessary for WiFi to work?
3. How does the interenet signal get from the building to your computer?
I will continue to research on my own, but all help is appreciated.