can someone direct me on the ways driven element of a yagi is attached
to a boom. can a driven element (folded dipole or ordinary
dipole)electrically connected to a boom or not? what will be the
effect? or can i use wood as a boom? can someone also give me some
formula on yagi design (length, spacing etc)

Just do a Google search on DL6WU - you can download the design program
and go from there.
Alan
VK2TWB