hello can some one help me by explain how to install a brush into gimp using windows 8..i downloaded the brushes but wen ever I click to open the file it opens as a picture...what should I do

You need to place any brushes you get for Gimp into Gimps 'Brushes' folder. If you click on them, they will open as image in Gimp.
I don't know the location of the Gimp Brushes folder on windows 8, but I'm still using windows XP and mine is located at... C:\Documents and Settings\myusername\.gimp-2.6\brushes.
If you can’t find that folder, see if it’s here instead: C:\Users\myusername\.gimp-2.8\brushes
You can also try this... (my computer > Local disk > Program files > GIMP 2 > share > gimp > 2.0 > brushes)
I'm also still using Gimp 2.6.11.

BTW... This type of post really belongs in the 'Gimp Help' section.

Moved to help.
Yes all your brushes you add to GIMP should be placed in the C:/Users/USERNAME/.gimp-2.8/brushes folder. This way when you update the resources will not be removed along with the un install. All other resources should be placed in these subfolders also.
scm files - C:/Users/USERNAME/.gimp-2.8/scripts folder
exe and py files - C:/Users/USERNAME/.gimp-2.8/plug-ins folder
brushes - C:/Users/USERNAME/.gimp-2.8/brushes folder
patterns - C:/Users/USERNAME/.gimp-2.8/patterns folder
gradients - C:/Users/USERNAME/.gimp-2.8/gradients folder
palettes - C:/Users/USERNAME/.gimp-2.8/palettes folder