Before this, i only know how to do a normal search string and searching for the string through the whole document. Now i can search and replace all.. Yay!

First occurrence on current line:      :s/OLD/NEW
Globally (all) on current line:        :s/OLD/NEW/g
Between two lines #,#:                 :#,#s/OLD/NEW/g
Every occurrence in file:              :%s/OLD/NEW/g