Well, sometimes you don't want to run your mongodb installation as a windows service, and you don't want to initiate it each and every time when you start your pc. Well under windows you can create a batch (.bat) file. It is that easy:
Put this line (logically change the paths)
start pathtomongod.exe --dbpath pathtodatadirectory
Save as yourpreference.bat
Put where it is easy to run and done!