What exactly is an amp head and what is its purpose when u can just buy a regular amp?....Do these "Cabs" have something to do with it? When i go on-stage to perform for a concert I just see a plug below me and hook my guitar to it....I never really asked about the amp equipment beacue it was always loud enough or soft (depending on what song) enough. Also recommend some cabs or heads or w.e. they are.
I never owned a stack amp, but most heads have replacable tubes in it, which gives the amp a good loud tone, especially when distorted. There are some cheap solid state heads that don't use tubes, but they may lack tune. The cabs are the speakers to play the head through.

I'd prefer buying a Marshall TSL or a Mesa Boogie Rectifier (both tubes)

For soilid state, a Line 6 Spider II is a popular one (mostly for effects), but I want to test out Fender's MetalHead amp; a amp that goes up to 550 watts and is suppose to be as loud as hell.
The head is the actual amplifier, the part that processes the guitar signal. The cab is the enclosure that houses the speaker(s), which in turn emit the sound. You won't be hearing anything from just a head or cab, you need both in conjunction.

What you refer to as "normal" amps are actually called combo amps - a head and cab in one, portable package.

And simply having a head has no impact on whether your amp is tube or not. Some heads are tube, some solid state. It's the same way with combos.

The major benefit of having a head is that you can switch out the cabs. Some would also suggest that heads produce a better tone than combos, but that's very debatable.

Likewise, combos are very portable and are thus preffered by many.

For recommendations... what music do you play? And whats your price range?