Snail-Po is a brand of Snail Food, which is not recommended for people that aren't snails. It's most likely a play on words of the Alpo Cat and Dog Food company.
Snail-Po is used to feed the snails of Bikini Bottom, but most snails don't seem to enjoy the food, including Gary the Snail, as seen in the episode: Have You Seen This Snail? (Though he is still seen eating it or at least willing to). But Gary would much rather eat cookies and nachos, and the comic in the Nick Magazine All-Animal Special, where he wants only the finest foods possible. It has an awful taste according to SpongeBob after tasting it in Missing Identity. SpongeBob is possibly the first person in Bikini Bottom to eat the Snail-Po. The Snail-Po was first mentioned in Missing Identity. SpongeBob has been known to not like it but it is unknown if any other citizens dislike it.
There is a Snail-Po headquarters where people make it, as seen in the episode Missing Identity. It is located somewhere in downtown Bikini Bottom, and look like most big corporate companies. We already find out from that episode that one of the peoples names is Peterson (Snail-Po Employee), who is most likely the guy in charge and one of the two people in the company that talked. When SpongeBob vomited upon tasting the Snail-Po, his cry reached the headquarters (Peterson heard him and when a woman in the company asked what was wrong, he says "I don't know, I feel... a disturbance). After that, we never get to see it again.