How to Share a MacBook Internet Connection

Click on the Apple menu in the upper left corner of your screen and select 'System Preferences' from the drop-down menu.
Click on the 'Sharing' icon within System Preferences, then check the box next to 'Internet Sharing' from the list of options on the left side of the screen.
Select the Internet source you want to share from the drop-down menu next to 'Share your connection from,' then check the box to the right of 'To computers using' for the Internet sharing option you want to use. Options include sharing the Internet through your MacBook's Ethernet port or broadcasting it through your wireless card.
Click the 'Airport Options' button to configure your MacBook's Wi-Fi network name and password if you are sharing an Internet connection wirelessly.
Connect the devices you want to use the shared connection to your MacBook through your chosen method. Either connect the device through an Ethernet cord to the MacBook's Ethernet port or connect to the MacBook's wireless network.
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How to Open a Port on a MacBook

Click 'System Preferences' from the Dock and select the 'Sharing' icon.
Check each box to enable sharing for the type of content you want to share. For example, check the 'File Sharing' box to enable File Sharing.
Select the 'All Users' radio button to allow access to anybody. Select 'Only These Users' to allow access to only the listed users. If you want to add users, click the '+' button, select a user or group from the Users & Groups list and click 'Select.'
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How to Share a MacBook With Another Laptop

Select the “Apple” menu in the upper left corner of the Mac OS X desktop. Select “System Preferences.”
Select “Sharing.”
Place a check next to “File Sharing” (by clicking the box) to turn file sharing on. Make note of the “Computer Name” as this is what the MacBook will be listed as over the network.
Click the “+” button beneath “Shared Folders” to add the folders you’d like to share over the network with the other laptop computers. By default, the “Public” folder is shared.
Select “Options...” and then enable “Share files and folders using AFP” to easily share your files with other Apple computers over the network. If you are planning to share your files with a Windows computer, enable “Share files and folders using SMB (Windows).' You will need to enable a user account for Windows sharing. Turn on the account you wish to share (by clicking the box) and enter the password as prompted. Click “Done” to apply the changes and close “System Preferences.”
Select “Network” from the Finder’s “Go” menu bar on the laptop you are using to connect to the MacBook you just configured. The MacBook will be listed and accessible for file sharing (provided they are on the same network). Open “My Network Places” (or “Network” in Windows 7) within Windows Explorer to view and access the MacBook from a Windows machine. You will need the user account and password to gain access.
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