On a Mac, you can make GIF animations without downloading any additional software. GIFs are useful in presentations or on the web when you need a small file size or low bandwidth option.
To make a GIF, you will need the image frames that you want to animate and Preview, which can be found in the Applications folder. I have made a quick video showing how to do this.
Creating GIFs using Preview on Mac from Benjamin M Ridgway on Vimeo.
However, please note that this will make a GIF that will animate only once. To make your GIF loop endlessly, you can use the image editor GIMP.
A Chemist Abroad 