Answer to question one: You need to click on the icon in the dock. It will start bouncing. When the bouncing stops, the application is active. That is how you launch Mail
Answers to question two: It's called e-Mail, and no, you don't need to pay postage. No, there is no need to place a stamp on your monitor. Click SEND to send the e-Mail. Yes, your friend at the other end will also need some type of computer and his/her own e-Mail address. No, the post man will not deliver e-Mail to you.
Answer to question three: That email was a pyramid scheme. You will not be receiving 20% of $5,000,000,000. The bank account information you gave and the $5,000 that you sent them "in good faith" were most likely stolen.
Answer to question four: Yes, receiving child pornography in your e-Mail is just as illegal as the child pornography you have on tape.
Answer to question five: No, other users can not see you through your e-Mail.
Cheers!