hi. i am trying to learn vop sop but i cant learn it fundamentally . and tuts that i downloaded from cmivfx and other site not simple for me and i dont understand for what reason the mentor of tuts create nodes . please give me a way and or a tuts that i understand the reasons of creating this nodes. thankyou

Wow, I am quite surprise you are having a hard time finding good tutorial on the basics. they are so many out there.
I will recommend Ben Wats melting angel:
https://vimeo.com/122217238
[vimeo.com]

Or check out basic training on Digital Tutors.
They are really basic but give good explanation on the fundamentals.

Good luck.