At the very top is a drop down letting you choose a CrushFTP server to control.  In most cases you will not need or use this.  This allows you to choose another copy of CrushFTP running on a remote machine (or the same machine) that you want to administer.  When you select an item in the drop down, CrushFTP will launch another copy of itself to connect and control that server.  This is the remote admin feature of CrushFTP.

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You can manage this list of items by clicking the "Manage Servers..." button.  You can add a remote server item here.  If you want this instance of CrushFTP to try and connect automatically at startup to a server, check the appropriate checkbox to do so.  If CrushFTP tries to start and it fails to connect for some reason, it will toggle this option off so the next time you run CrushFTP you can fix whatever is wrong in your configuration.