Cool beans is an interjection of approval. If you really like something or think it's pretty nifty, you might say, "Cool beans!" — which might sound a little retro, but hey, you'd fit right in if you time-traveled back to the 1980s!
Cool beans — like wow or wicked or groovy — is the kind of thing that you might say when someone does something you think is great, exciting, or interesting. This slang term was first recorded being used in this "wholesome vibe" way in the late 1980s, when the character D.J. Tanner in the sitcom Full House used it as a catchphrase to mean "great" or "sounds good." That makes it younger than groovy but older than lit, massive W, or absolute gas.