There are some quick methods you can use to open a source file.

In the Browser Window, click the Open File icon when portions of the file you wish to see are displayed in the window's Source pane. See "Open File icon" for more information.

To select a file, click on a symbol used in that file. Then use the Browser Contextual Menu to open the desired file or see a particular routine.

If you are looking at a source file, and want to see the interface file, or vice versa, simply type Ctrl/Command \Q to see the related file.