The answer to the first question depends on whether you use the gem compass or compass.app. The application gives you a drop-down list from the menu on the poppy, and you can do everything from there. The gem requires you to tell him to view the folder from the command line. In addition, you do not need it to work in the application. Sass is compiled in advance and output as CSS to the folder created during installation.
Here is a page containing basic information for launching the compass and Sass.
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