If you buy the standalone unit you connect it to your TV via HDMI and then you have two choices for getting the content onto the TV.
1. Plug in USB HDD to the PlayOn.
2. Connect the PlayOn to the same network your laptop is on, share the folder on your laptop then the PlayOn will find it. You can do this via ethernet or buy a wireless dongle for the PlayOn.
if you want to stream HD stuff (720/1080p) you won't be able to do it over wireless. You will either have to have the media stored on a USB HDD or have the PlayOn and laptop connected to a router/switch via ethernet cable. One of the main reasons I went with the PlayOn over the Apple TV was the interface, ease of use, and the fact that out of the box it can play pretty much any file type(avi, mp4, wmv, mkv, iso).
You can also go for the standard version which can house a 2TB HDD, I have the mini as my stored media is elsewhere.