LOL! I didn't get it at first, and then I did. (You have to choose a type of lemming from the list of abilities at the bottom--the low levels give you only one choice or two, effectively telling you what to do--and then click on one of the marching lemmings to give it that ability. If you want them not to march off a cliff, click on the first one to make him a blocker. If you want them to dig a hole down to the next tier, make one a digger or a miner.)

And then I found that fast-forward didn't work for me, so once I'd got them marching home, there was nothing to do but wait while eight thousand and seventy-two (okay, fifty) lemmings slowly marched home. Which is fine when you're multitasking, but...protracted when you're stoned and just staring at the screen.