1) Download the Webshots installer at, webshots.com/desktop, by clicking the "Free Mac Install" button.
2) After you click on the "Free PC Install" button, you will see the .dmg file shown on your browser. Using Firefox, it will appear on the top right of your browser screen. Using Chrome, it will appear at the bottom left as shown in the screenshot below.
3) Once downloaded, open the .dmg file. You will then get the following Finder window:
4) Drag the Webshots file to the Application folder. You should then see Webshots in the Applications folder: