Can someone breakdown to me in as much detail as possible the structure of how to put a beat together. Extremely detailed if possible. What i am talking about is not intro-chorus-verse...blah blah blah... im asking for beats per bar for a drum pattern, how to start a drum pattern, melodies, hook, what is a hook, how the different parts of the song sound different, bridge, what is a bridge, yet stay in the same key and use same notes, bassline, layering, harmony and how it all fits together. If there are any books plz recommend. I really just need to figure out were and how to start composing the hip hop track.

Thanks
Typical beat.
Intro (4-8 measures)
Sometimes Chorus before the first verse sometimes only 4 bars of chorus before the first verse, sometimes the chorus is the intro, and sometimes it goes from intro to first verse.
In a typical song, a verse is 16 measures. Sometimes though it can be 12, and in many songs that involve lots of features, it may go up to 24 measures. Now, a verse may also be 24 measures long, but only counted as 12 "bars" because the tempo may be at or above 120 (beats between 106-119 BPMs usually suck by the way, it is a dead zone). When beats are at or above 120, they are usually done in half time. This means that the beat may "sound" slow because it takes two measures to complete the "bar" with the snares hitting on the 3's of each measure (step 9 instead of steps 5 and 13 on a step sequencer). Songs done in half time usually go 12 "bars" (24 measures) because of pacing issues. Though these songs still tend to stick with 8 measure hooks that go by fast.
Then chorus (sometimes 8 measures, sometimes 12, either for regular or half time songs)
Then verse
Then chorus
Then verse
Then chorus
Then outro.
Many songs in halftime, or that have features may have more or less than the usual "three" verses. Sometimes hooks get repeated at the end an extra 4 or 8 measures as well.
A Bridge is something that usually comes after the second chorus and before the last verse, or after the last verse and before the last chorus. They are usually 8 or 12 measures (Usually 12 to 16 measures for half time beats). These are not basically breakdowns or massive melodic changes in the beat placed generally in the two areas described above, at the producers discretion.
As far as melody changes, those are good within verses and for choruses (HOOKS as some call them) and remember than you can also have lots of instrumentation going on and simply drop things in and out every four bars. The less instrumentation in the song that is used, the more varying melodies need to be used to keep it from being boring.
Key changes are Producer's discretion, sometimes they work, especially for bridges, and sometimes they don't. It depends on from what key to what key though. Sometimes they are dramatic, sometimes they sound out of place. Melody switch-ups should be considered before key changes, and usually key changes are not necessary unless it is a dramatic or orchestral sounding beat.
Before I really found my "signature style and sound" over the years, I began with the 5-7 rule.
This meant that for each beat I would only use:
5-7 drum and percussion sounds
and
5-7 instrument and/or sample sounds (whether used sporadically, all at once, in and out, or even only one time in the entire song)
Anything over that in either category was letting the song get away from "good drum and instrumentation" to layering for layering's sake to cover up bad or boring instrumentation (as in melody, sound/synth effects and noises, harmonies, etc.).
I still kind of go by these rules 90% of the time, and only break them when I have a darn good reason to (usually like when a beat has heavy orchestral sounds, and still, most when I use those sounds I don't go over anyway), and the situations which beats break those rules can only be known from experience more than anything else.
Hope this all helps.