Not to be annoying, but RTFM. That's why I suggested it in the first place. Saying split(1) is Unix shorthand for saying "there's this feature called split and it can be found in volume 1 (external commands) of the Unix manuals, such as typing man 1 split or just man split."

If you read the find man page, it explains that it will replace the {} with the currently found filename, and the \; is to terminate the -exec switch argument. (It's looking for just a ; but the shell would eat it if you don't escape it.)

Why two {}s? Read the other man page to see how split(1) works. It needs the filename to split, and we give the name again as a prefix argument to give to each split output.