Like most blockchain based digital currencies Stellar has a public and a private key. The public key always starts with ‘G’. The private (or secret or seed) key always starts with ‘S’.
Here’s my public tip address: GBUEOYQGCQSZ2CS7OODRVAYIOFW56OG3W43SVTPNVM7OJZSPCMZUW4AJ
One other unique item is that Stellar accounts must be created and funded from another account before it can be used. Just having a public/private key pair is not enough to use the account, it must be created first.
As of January 30th, 2018 there have been 308510 accounts created.