Most VST(i)s have completely different interfaces from each other, so it's hard to give a tutorial to using them. However, I generally find that the best way to start getting sounds out of them is to play with the presets, and spend a little while twiddling various knobs to see what effect they have. Try starting with simple VST(i)s - the ones at
tweakbench are nice and simple, and have a consistent interface. They're not the most powerful, and don't always produce the best sounds, but they're still very solid little instruments and effects.
Are there any specific plugs you're having problems with?