Regulars in each group get annoyed when these questions are asked again by newcomers, so it's well worth looking these over. In net speak, trolls are information that looks sincere and convincing but is a deliberate attempt to wrong-foot people and get them to react violently. The authors of trolls always think their work is amusing, and to be fair some trolls are on a par with the best published satire. But many trolls are simply annoying. There's no sure way to spot a troll - you simply have to keep your wits about you.
Flame wars are long angry, abusive conversations with little useful content.
Sooner or later someone will post something that outrages you, and you'll be tempted to disagree with them loudly and violently. In a word - don't. You could find yourself part of a flame war, doing battle electronically with one or more foes for anything up to years at a time - much to everyone else's annoyance and disgust. As a rule passionate postings get passionate responses. People will respond to the tone of your posting much more than to its content.