They say that a picture is worth a thousand words so whenever I create an issue, a pull request or write a blog post about and application or some visual stuff I include a relevant image. Sometimes an image is not enough and an animation is needed to better describe the issue, or show the content of your pull request.
There are some good tools to help you to create animations like this on both Windows and macOS.
ScreenToGif is a simple but powerful portable Windows app that helps you record your screen and save it as a Gif. You can record the whole screen or just a custom window. This is ideal for example for recording the behavior of your apps in an emulator, recording just the emulator window.
To create app animations from the iOS simulator on macOS I use Gipphy. It is a simple app that works similarly ScreenToGif. There is no need to upload your Gifs to the Gipphy website, you can just save them locally.