Change to normal mode with <ESC>.

Search (Wraped around at end of file):

  Search STRING forward :   / STRING.
  Search STRING backward:   ? STRING.

  Repeat search:   n
  Repeat search in opposite direction:  N  (SHIFT-n)

Replace: Same as with sed, Replace OLD with NEW:
 
 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

http://www.felixgers.de/teaching/emacs/vi_search_replace.html

VI - Search and Replace

search, replace

Bash