Flags, keys and stuff.Follow

My toon is currently level 40 and I keep reading about people having this flag or that key, what does it all mean?. Is there anywhere that gives all the info on the flag/key system.
On anougher note at my level lots of groups are in The Dreadlands and to get there I have to go through the tunnel in FV. I am an Iksar and every time I set foot in the tunnel some stupid Elvan dude makes mincemeat of me. My question is, can this Elvan dude see invisible if I used a cloudy potion to get past him?

For the run from FV book to Dreadlands, yes invis works fine. I run my necro through there all the time.