so if i want to create a tune let's say in C major key then normally i'll have to use these chords:C,Dm,Em,F,G,Am and Bdim. what other chords can i use? like sus,M7,m7 and so on? is there a some sort of pattern or what?
Well I'm no theory wizz but yes, I mean, you're th eone making the music. Jjust use suspended chords and add the 7th if it sounds good, especially if it's still in key, may sound fuller...
*shrugs* I don't know...
this is a pretty hard to explain question. all chords are based on a scale. such as c major is c,d,e,f,g,a,b (1,2,3,4,5,6,7) while c minor would be c,d, Eb,f,g,a,b (1,2,b3,4,5,6,7). check out cyberfret.com for a list of all the scales for each type of chord. hope this helped some.
look at the mode for each chord. if a major 2 is in that mode, you can play a sus2. likewise, a perfect 4 - sus4.

it'd be Cmaj7, Dmin7, Emin7, Fmaj7, G7, Amin7, Bmin7b5.
basically, a major 3rd will make it major or dominant. the b7 makes it dominant.
a minor 3 makes it minor or diminished. the b5 makes it diminished.

you can do the same thing with 9s, 11s, and 13s. just look at how they're formed inside the modes.
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These are generally the most common chords..

I: _maj7, _maj9, _6, _6/9
ii: _m7, _m9, _m11, _m13
iii: _m7b9, _susb9
IV: _maj7, _maj7#11
V: _7, _9, _sus, _9sus
vi: _m7, m7b13
vii: _ø