Some times you need to try apps before installing them on your phones, or you don't have an android phone but you want to play Android games, so you are in the right way to do what you want :D
The are four ways to run android on your computer :
1# BlueStacks
It's the best way to run andoid system on your phone. It workes inside your system (windows or linux) so you can use it without worry ;)
From here: Download BlueStacks
2# Officiel Android Emulator
It's like the BlueStacks the one only difference is that this one's from google ( part of ANDROID SDK ).
From here : Android emulator
3# Android-x86
From here: Android x86
4# Android on Intel Architecture
This is a good way from intel, you can install android beside your windows 8 or 7 if you have an Intel prossesor.
From here : Android on Intel
If you have any question please comment.