Load your video, trim to the section you want, set the frame rate and width, and export — the animated GIF downloads ready to share.
GIF is an old, relatively inefficient format — reducing the frame rate (10-15fps is usually plenty) and the output width (400-500px for social sharing) are the two most effective ways to shrink it.
Yes, set the start and end points on the source video first so only the section you want becomes the GIF.
Yes, standard animated GIFs loop by default in every browser, messaging app and social platform that supports them.