[you find the tombs when you reach the third or fourth town you gotta climb the viewpoints and the tombs will be marked as AC]
Pay attention to your HUD - Whenever a building that will have a Glyph or Tomb will show up with a Red Eye - Use Eagle Vision to fin either...
Also, mycheats.com has a pretty good guide...
Chat with our AI personalities
They show up as icons on the map as you play, you never really have to search for them. You can't find them right from the start, they have to be introduced to you after you do a certain amount of story missions. Their icons are the same symbol as the Assassin's Creed symbol.