Not that I don't know the difference between what they are and various exercises one can perform with each, but what would you say the respective advantages and disadvantages of each are? Currently, I just have dumbbells and wonder if there are some things I will need a barbell for. I realize that dumbbells are going to force each arm to act alone whereas a barbell will require the arms to work together, but how will the difference affect my muscle development? Also, regardless of what I'm suing, how can I decide what I can safely do withou a spotter and what requires one? Thanks.

I use dumbbells for just about everything except skull crushers, i use a small barbell for that, one of those curved barbells. Otherwise I use my dumbbells even for my bench press because i broke my left wrist so now its not as stable, so i fear that if i have a bar across me and my left wrist gives out, i would drop the bar on myself, but with dumbbells i could just drop the dumbbell with less risk of injury. (Which has happened to me once, but once is enough to do some damage) as far as muscle development, supposedly because of the extra balance and stabilization that dumbbells require its even better for the muscles. I think you'll be fine.