WebP animations keep more colour than the 256 a GIF is limited to and are typically much smaller than the same GIF, so pages that use them load faster. Current browsers show them; some older editors, email clients and chat apps still need a GIF.
The defaults suit most files. Under Options you can set the frame rate, set the width, trim the start and end and set the quality. This is demanding work for a browser: a long or high-resolution file can take several minutes, and your device does all of it, so keep the tab open.
This pair uses the compatibility engine, ffmpeg built for the browser, because GIF is not handled by the browser's built-in codecs. It is a one-off download of about 10 MB that the browser keeps, it is slower than the built-in codecs, and it takes files up to 1 GB. The result is a looping animation of at most 30 seconds, counted from the start point you set under Options. The GIF's own frame timing is kept unless you choose a frame rate, and the picture is scaled down to 480 pixels wide at most, never enlarged. Unlike a GIF it keeps full colour, and it has no sound.