It's a shame that they don't provide any explanations. This literally means: "Over there!" Because you call for the waiter who is typically "over there". You could also call "여기요!", "over here!" to draw the waiter's attention to you "over here". This explanation would also help understanding when you could use this in other situations. If you are looking for something with a friend. And you found it, but the friend still doesn't see it, you might point at it and say "저기요!".
While 저기요/여기요 is a typical way to call a waiter in the South, it is considered rather rude to do so in North Korea. One is expected to yell "접대원동지!" or "접대원동무!" in a North Korean restaurant. 접대원 means "waiter" (only in the Northern standard!), while "동무" and "동지" translate to English as "companion" and "comrade" respectively. Comrade waiter!!!
Edit: a shortened version fo this call also exists: 접댄동무!
Naturally. I got this particular fact from this blog thingy LINK. It's a blog of an Australian student who attended a N. Korean university, an interesting read overall. Very ufortunately, he got arrested and expelled from the country because of his ties with anti-NK media around one year ago...
Here LINK is an English-Korean dictionary from N. Korea which someone ripped from a NK brand smartphone and uploaded to the Internet. With it, you can see that 'waiter' is indeed "접대원" in NK.
Finally, I got that "접댄동무" part from a NK film "Ask Yourself" LINK, timestamp 39:38.