A homegroup in Windows 7 makes it easier to share files and printers on a home network. You can share pictures, music, videos, documents, and printers with other people in your homegroup. As a security measure, other people cant change the files that you share, unless you give them permission to do so.
When you set up a computer with Windows 7, a homegroup is created automatically if one doesnt already exist on your home network. I assume that you already have an existing homegroup in one of your Windows 7 computers. If a homegroup already exists, you can join it. To connect a second computer to the homegroup go to the first computers control panel, then click
HomeGroup:

After you create or join a homegroup, you can select the files and folders that you want to share. You can prevent specific files or folders from being shared, and you can share additional libraries later. You can help protect your homegroup with a password, which you can change at any time.
Click the view or print the homegroup password to view the password:

The password will appear. You may opt to print it and distribute to other people connected to your homegroup.

One your other Windows 7 computers, go to the Control Panel > HomeGroup then click Join Now:

The concept of homegroup simplifies the file sharing on small scale home networks. In older versions of Windows like 2000 and XP, users had to supply a login and password for another machine or map a network drive to access shared content or devices.