thanks Mike, glad you found it helpful! Basically, SBD is more or less pegged to the US Dollar (should always be worth about $1 USD give or take), which is redeemable at any time in STEEM worth approximately $1 USD. STEEM is the base currency that signifies one's stake in the system (when converted to STEEM POWER), which can also appreciate or depreciate based on demand and adoption of the STEEMIT platform and blockchain itself.