Best Place To Download It: http://www.minecraftforum.net/topic/249637-174-optifine-hd-d1-fps-boost-hd-textures-aa-af-and-much-more/ (http://www.minecraftforum.net/topic/249637-174-optifine-hd-d1-fps-boost-hd-textures-aa-af-and-much-more/)
once you download that, you should get a java file. double click that and is should open a small window asking if you would like to install it. click install and then it's done.
open minecraft, Profile: optifine (should be there) then play :D easy as that