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.
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.
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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.