You don't lose your souls completely, where you died and lost your souls, you leave behind your "blood-stain" go back this and you'll regain all your souls once again. It's just a motive to get you to play back through the level to overcome that obstacle. When you are connected to the network, you also see other "blood-stains" on the ground, which when you touch them, you can see how the previous player died. It's handy to know if there is a trap ahead, or a group of mobs ready to rape you, along with user messages all over the place.
I noticed on my first play through, there is a small element of grind required as you wont be powerful enough to take on most bosses right away, even through you can play right up to them.
Another thing, there are ways around this game being stupidly hard, for example, level up your bow and arrow, this makes pretty much all bosses pretty simple in the game, but I don't recommend doing so if you want a true challenge, and purely melee'ing some bosses you will purely end up with your ass handed to you most of the time, but it's all a big learning process.
You wont have any black phantoms till later on in the game, so you don't have to worry about that right away either. By the time it happens you should be slightly more prepared for it. And can reap the rewards of destroying an invading player which lets you keep all there souls, unfortunately, if an invading player kills you, they take all your souls, so you have to stay on your toes. There are a few items that let you mask yourself from invading players, and you can hide, they sometimes give up there chase if you are far enough through the level.
Oh and here is that wiki link:
http://demonssouls.wikidot.com/
