Compressing files into the ZIP format on your Mac reduces their size, but a zipped file isn't much use if you can't open it. Macs running OS X Yosemite have native support for extracting ZIP files. All you need to do is locate the file and click it.
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Opening ZIP Files
To open a ZIP file your Mac, click the "Finder" app on the Dock and browse to the location where the ZIP file is saved. Double-click the ZIP file to extract its contents. The contents of the ZIP file are automatically extracted to a new folder with the same name and in the same location as the ZIP file. Open this new folder to view its contents and access the files contained within it.
Compressing and Troubleshooting
To compress a file and save it in the ZIP format, hold down the "Control" key, click the file and select "Compress" on the pop-up menu. The compressed file is automatically saved in the ZIP format in the same location as the original.
If you attempt to compress a file and can't, you need to change the file's permission settings. Select the file and press "Command-I" to view its information window. Expand the Sharing & Permissions section and change the permissions for the file to either "Read Only" or "Read & Write." You may be prompted to enter your Mac's administrator password.