The Krusty Krab is the restaurant where SpongeBob works. Its one of the most successful restaurants in Bikini Bottom and is famous for its Krabby Patty, the most popular burger in Bikini Bottom. Problem is, it doesn't have many employees. The only employees that work there are Squidward (the grumpy cashier) and SpongeBob (the fry cook.)
The Krusty Krab doesn't just sell the Krabby Patty, here are the other things you might find on the menu.
Double Krabby Deluxe
Double Chilli Kelp Fries
Nacho Oyster Skins
In the past Mr. Krabs has done many things to The Krusty Krab. In "Culture Shock" a talent show was hosted there, however it didn't do too good until the end of the show. He also once did a Joke Night (The Komedy Krab), which ran on for several evenings. It was turned into a fancy restaurant twice. The first time was in "Squilliam Returns" when Squidward wanted to impress Squilliam by making him think he owned a fancy restaurant. The second time was in "Le Big Switch", however things didn't go too well. In "Krabby Land" he added a playground, but the playground was rubbish. He added "The Krusty Pool" in the short, "The Endless Summer." In "Krusty Towers" it was turned into a hotel after Mr. Krabs learned in hotels you could charge so much for a burger. In "Born to Be Wild" Mr. Krabs added some Biker Gang stuff to get the Bikers to The Krusty Krab.
In "Krabs a La Mode" it was turned into an Ice Rink and later a swimming pool. In "Bucket, Sweet Bucket" the inside was redecorated by Squidward and new features were added to it like a fountain and a computer, also prices were raised a lot. Also, The Krusty Krab was "SpongeBob-ified" and renamed "The Krusty Sponge" in the episode with the same name. Also, in "Mermaidman vs SpongeBob", the restaurant was "Mermaidman & Barnacleboy-ified."
It is possible that Mr. Krabs had once turned The Krusty Krab into a hospital, as in the end of "Krusty Towers" he told SpongeBob, Patrick and Squidward they're going to medical school.