This is the main window of Easy Thumbnails which allows you to browse for a folder in which to look for a specific type of images. You may preview each image on the right panel 

The Settings tab displays a list of adjustments that you can apply to the selected image, like JPEG Quality, Brightness, Contrast, Sharpness and Rotation. In the right panel you may see the preview output 

After selecting and editing a specific image you must add an output folder in which to save the thumbnail and simply press the 'Make' button. You may also transform all the images in thumbnails by pressing the 'Make all' button