Setting default application

When you double clicks a certain file, it will open a corresponding application for this type of file. For example, you have Microsoft Excel application installed on your Mac, and everytime you double clicks the *.xls file, the Microsoft Excel application launched. But you want the Number application that opens this *.xls everytime you double click (or Command O) it.

First, you have to go to Finder, and look for any file that has an extension of xls. Click once and press Command + i (or right click and select Get info).

Second, select the ‘Open with’ drop down menu and choose the application that you wish to open this xls file. In this case, we choose Number application. Then under ‘Use this application to open all documents like this’ press ‘Change All’ button.

So now you have a default application for certain type of file.