How does multiplayer work? I have a couple friends that want to play together, but from what Iv read it's not easy to set up with specific people.
It isn't too hard to meet up - I've done it a few times with CAGs. You just have to arrange a meeting place and have one player set down a blue stone marker (indicating you want to be summoned). The thing is, any player online could select that and summon you. If you choose somewhere off the beaten path, though, you minimize the chances for that. The player you join can still be invaded by a black phantom too - but then it is pretty fun to surprise an invader when you have 2 players to gang up on him. That happened to Chibi and me, I think, a few times while he was letting me "borrow" various weapons. We pretty much wiped the floor with them. I guess if you have 2 people visiting, though, there's no room for an invader?
I had just started my third playthrough and the ideal place to put an out-of-the-way marker is the little alley just past the 1-2 archstone where Ostrava is behind bars.
OK, more is coming back to me... To put down a blue stone you need to be in Soul Form (as I always
was while playing). The person summoning has to be in body form, though. And I think they have to have not completed the level they are trying to summon you on (not 100% sure on this though). So you need to make sure they have access to, but have not yet beaten, the level you want to join up at. If the person in Soul form leaves the current level I think they just end up going back to their world. Also, as a blue phantom you don't lose any souls if you die. If you are an invading black phantom you do though - and the players who killed you share them.
By the way, if you are around mid-game and know of a particular boss that you think you can handle pretty well (say, the Tower Knight or such) then you can place a blue stone right before the boss fight and hopefully someone will summon you in to fight that boss. You get a nice amount of souls as a reward with no risk (you won't lose the ones you have if you die). It is a great way to gain some levels mid-game when you need it most. I did this quite a bit. As you get up to level 100 and beyond, though, you will generally be too high a level to get summoned by most people (as most probably are looking for help earlier on - plus, of course, there are probably more low-level people playing).
Another point is that you can only connect with people fairly close to your level. Someone way back posted the specifics but I think you have to be within 10 levels below 100 and then 25 afterwards? It's something like that, anyway - so to meet up with your friends you have to be close in level.