I downloaded MiKtex 2.9 for windows 8 64 bit, but I can't find out how to run that software as there is no shortcut on desktop or on the APP page. If any one has used Miktex on windows 8 OS then please help me on the issue.
MiKTeX includes TeXWorks, a (basic) editor for (La)TeX. If you search in windows 8 you'll find it. Sometimes apps/programs don't get added to the start screen, so manually pin this to start.
Other options are to use your own favorite text editor(check the list at LaTeX Editors/IDEs for good editors) and use the commandline to run
pdflatex document.tex or
texify -p -b document.tex(-p for pdf, -b for non-interactive mode).
If you need a syntex-file, use the following command with texify:
texify -p -b --tex-option="--synctex=1" document.tex.