This is the first collection of Squirrel Girl comic books published as a graphic novel. It includes Squirrel Girl 1-4, plus the first Marvel comics story featuring her, The Coming of... Squirrel Girl! (Marvel Super-Heroes (1990) #8).
Squirrel Girl is a very minor heroine in the Marvel Universe -- or she was until just recently. She has spruced up with modern artwork and better dialog, entered college, and started beating up the big supervillains. She has witty banter, a solid foundation in scientific literacy, and a full set of supervillain reference cards. And she's not afraid to use them.
These first four issues follow her moving into her college dorm, meeting her equally-nerdy roommate, meeting a cute guy, and beating Kraven, Galactus, Whiplash, and assorted bank robbers and muggers in her spare time. To be honest, there's not any more of a plot than there is in the average Marvel comic (disclaimer; I actually have very little experience with comics of any sort, so this may not be true), but the writing and characters are much less stilted than the traditional comic. I base this largely on the reprint of the 1990 story in which she first appears, trying to sign on as Ironman's sidekick -- which was really pretty awful.
Given that there's not much of a plot to describe and that spoilers are bad, I will simply say that Squirrel Girl is half Squirrel, has a squirrel sidekick, and can talk to squirrels; she is always open to non-zero-sum outcomes and enjoys lampshading classic comic tropes. She is a hip young millennial nerd, and if she makes constant silly pop-culture references to comic book heroes this does not hurt her nerd-cred at all, as it is usually immediately relevant to her continued survival. Overall, a pretty decent read, and an excellent introduction to the lighter side of the Marvel Universe.
If you are not really into comic books but think you might like to check one out, I would highly recommend this collection. It is popular enough that I was able to pick up a copy at my local library, but it is also available at many book stores and comic shops, with a manufacturer's suggested retail price of $15.99. It is followed by a number of other Squirrel Girl collections, the next being The Unbeatable Squirrel Girl, Vol. 2: Squirrel You Know It's True.
Squirrel Girl is written by Ryan North and drawn by Erica Henderson. This collection includes art by a number of other illustrators, who designed alternate covers for the original comics, trading card art, and the original 1990 Squirrel Girl story.