Sorry about that last post, it was written by a friend who doesn't believe in the flat earth and doesn't understand how apostrophes are used, either.
I believe I can help you out, Mr. Pearson. I'll take your questions in order.
1. The walls of ice
This illustration should help explain:
Just to clarify, the "x" at the center is the north pole, and the red circle indicates the path of the sun. As you would expect, those areas further from the sun's path are colder: namely, the north pole and the "wall of ice".
As for why no one has seen them: plenty of people have. They've simply given them a different name: "Antarctica."
2. Getting your friends to believe
This is a bit harder; typically people who believe in the round earth are pretty set in their views and not very willing to change them. After all, they're the large majority at this point, and it's a rare person who will stand up in the face of fifty-to-one odds.
The trick is to lead by example. Let them see how knowledge has set you free. You're not buying into this shit anymore, and that's a starting point for not buying into all kinds of other shit. Just stand firm in your beliefs, and once your friends see the power it gives you, they might not be so skeptical anymore.
3. Standing up when questioned
Again, round-earthers are usually very resistant to changing their views, and this goes double for those that try to question you directly. Typically they're just looking to make themselves look smart at your expense. Until you understand some of the theory behind flat-earthism and can put up an intelligent argument, it's usually best not to get drawn in. Just tell them, politely, to fuck off, and leave it at that.
Hope I've been of help.