Homegroup is is a space where you can safely share and download files within your network computers. It is a shortcut solution compared to connecting through wires and ethernet cables. There is no hassel of wires, it's all virtual.
However, before sharing, you must make sure that all the computers in your network are not exposed to malware or other dangers, you should only connect with computers in your network which you trust.
If you have windows 7 then homegroup is already created, you just have to join it and start sharing it's that simple. Before joining a homegroup your network should be set to "Home" and not "Public", you'll come across that option in the joining process.
So, to join 'HomeGroup' simply click START-Type HomeGroup-Create Homegroup(if not already created)OR Click Join and complete the setup wizard.
Now for sharing, click Start- Select you user profile - then simply right click the file or folder that you want to share and click 'share with' Here's a snapshot,
Now you can share and receive media among trusted computers. Hope this helps. Thank you.