I don't know much about animations, but I believe/assume they are done with
animated GIF image files.
So it would seem you may need to start by collecting some animated GIFs you
want to use, then attach them to emails, the way you would attach any other
graphic image file from your computer's disk. You might need to use Rich
formatting (like HTML) in your email to make sure they appear at a specific
place in your messages.
Whether or not (a) Gmail allows one to attach animated GIF files, and (b)
whether Gmail displays them with animation when using their web interface,
are two questions I can't answer. I know Gmail doesn't allow certain
attached files because they could be used to transmit a virus; I don't know
if an animated GIF is one of them.
Andy