The words "snap" and "snack" are completely different.
A "snack" is something to eat that is much smaller than a meal. A candy bar might be a snack. An apple might be a "healthy snack."
To "snap" something can mean to break it in two. "He was trying not to make any noise, but he stepped on a twig and it snapped."
It can mean to make a noise like something snapping: "He snapped his fingers."
It can mean to do something very quickly, or easily: "This won't take long, it will be a snap."
An informal photograph, taken very quickly, is a "snapshot."
There is an app called "Snapchat."
"Snap" means quickly and easily, like taking a snapshot. A "chat" means an informal, friendly, quick conversation. "We were both waiting at the bus stop and we chatted for a few minutes until the bus came."
"Snapchat" suggests "a quick or instant way to start an informal conversation," and the company's slogan is "The fastest way to share a moment!"