I see you're reading Sherlock Holmes : A Study in Scarlet. You can understand 'our driver suddenly came to a stand' as meaning that he suddenly stopped the cab. It's an unusual phrasing, though, and we wouldn't normally express this idea in this way. I wouldn't worry about this phrase if I were you, because you are unlikely ever to meet it again. Just enjoy the story!

In modern English we'd be more likely to say "came to a standstill" meaning a "stop". At the time this sentence was originally written, the word "stand" was used to mean "an act of stopping or staying in one place." In American history we learn about General Custer's last stand. (See http://www.americaslibrary.gov/jb/recon/jb_recon_custer_1.html)