What did you try already?
You should install NodeJS first from www.nodejs.org
Install mongo or redis, depending on which one you would like to use. If you use a hosted service for those, then skip this step.
Then download NodeBB from github. I'd recommend to use GIT for that, but you can also just download the .zip in the releases folder.
If you use the ZIP: unpack in the folder you'd like to use it in.
If you use GIT: then you're ok now
Go to the folder you've got the NodeJS system files. Open command prompt in this folder.
Type "npm install"
Wait until everything is installed. If it fails, check if you've got the correct building tools installed to your OS (it should be if you're using windows 2008 I thought)
Type "nodebb setup", enter the details
If you're done, do "nodebb start" and nodebb starts
Next: in production you would like to set up a reverse proxy. Check docs.nodebb.org how to do this with windows IIS