most of those are kind of arbitrary. a hook is just the catchy part of the song, like the chorus, or a guitar lick, a vocal part,a structure, whatever. like the intro lead to in flames embody the invisible or soilwork millionflame. the parts that grab the listener and get stuck in your head. a riff is a guitar part. usually a rythm part. a lick is a lead line, or melody or something like htat. a melody is a melodic part of the song. like a vocal line in a power metal song. harmony can support a melody part by playing different notes to build of chord or a larger sound. iron maiden does this with guitars all the time. same with soilwork, in flames, whoever. even morbid angel, but they are more abstract.
bridge is a middle section of a song usually. doesn't work in more abstract or linear songwriteing, but it can be a lot of things. it bridges two parts together.
power chord is a root and a fifth chord on a guitar, sometimes with the octave. actually i guess i would be any diad chord. you could use root and third, whatever. usually its the fifth.
a blast beat is usually a really fast one two beat. there offset blasts, what i call the black metal blast, there are the cannibal corpse blast where you hit everything at once. whatever. just listen to suffocation or dark funeral or whatevr. its just something you have to hear adn you'll figure it out.
over dubs are a recording technique of just recording something after somethign else has already been recorded. you record all your rythm tracks say, and then you overdub the leads.
none of these are really set. there aren't real strict definitions for these, except maybe overdubs.
