New to this - what is google snippet?

two things get called that. the snippet is the bit of text under the blue link in a result, which google writes itself most of the time, often ignoring your meta description. the featured snippet is the box at the top that answers a question outright. what it's for from your side: write the meta description anyway, it gets used maybe a third of the time. and if you want featured snippets, put the question as a heading and answer it plainly in the two sentences right under it. that's it, no tool needed.