When building a website, how to combine multiple small images into a big one?

Hi, when I open google front page in chrome developer tool, I found that they have bundled multiple icons into a large png file and then download them together(as above). I think this is a somewhat common approach to accelerate page loading. Can someone point to me a how to do that? Better yet is there a library to handle the bundle/debundle?

(I spent quite some time online searching for this but can't find exactly what I need. Any help would be appreciated!)