You may save image with Save button.
You may save image selecting Save from File menu. (or using Save menu hot-keys)
You may save image by double clicking on cropping frame.
As an alternative you may drag image from the program's right panel (a panel with preview) and drop it into any folder in finder, or in any application that can accept dropped images. For example, you may drop cropped image into Mail application.
Click 2 Crop asks you for output location and filename only once, at the first crop in session. All sequential saved files are saved into the same folder with incremented name. There are two naming rules available. You may select to increment the name of the current file, and you may to select increment of a custom chosen name. These rules can be set and changed at Preferences panel.
If you want to change output location, you may bring up a save dialogue selecting Save… menu option. All following files will be saved into the new selected output location.
Sometimes, while saving a long photo serial into one location you need to save one "exceptional" file into some different place. In this case Save as… menu helps you. It brings up saving dialogue for only one file. That is your main output location will remain the same.
You may select a format of saving file (.jpeg, .tiff or .png) with save dialogue. All following files are saved with the same format.
You may to change output file format in the middle of the session with combo box at the bottom of the main program window. And, please don't forget that you may to invoke saving dialogue at any time with Save… menu option.
There are two more saving option at the bottom of the main screen.
Save EXIF - When this option is enabled program saves so called EXIF information (a special file section that keeps additional photo information like Camera model, Shutter and Aperture values, Focal distance and many more) together with output file. This EXIF section may add from 5 to 20 Kb to output file size. You may not care for this size increase when you prepare images for printing or hi-res online gallery, but you're preparing small thumbs for web site this unnecessary addition can be compared or even bigger than thumb file size itself. In this case it is better to disable this option.
Save Landscape - When this option is enabled the program saves all files in landscape orientation. That is width of image is larger that image height. This mode is very useful when you prepare your images for kiosk printing. There are printing kiosks that requires your images to be in landscape orientation. If you send them a portrait image, they will print it as small portrait with huge left and right white margins. Images saved with Save Landscape option will be properly printed even with these kiosks.