You can be attacked only by players with difference of +-3 levels from yours, no more. So you couldn't have been attacked by players 5-10 lvls above you. Actually it's a PVP game, so just be careful, don't stay in location for long when you see potentially stronger players, either attack npcs, run to other location or go to lobby. Following this simple rule will save you from unexpected PVP most of the time.
Full screen might not work on some Intel video cards. You may try to update your video drivers, in order to fix this issue.
Share with your friends is often on lower levels, you will not see it much on higher levels.
This is only offered if you perform any quest or competition.