Ok, I understand. Buying Steempower with Steem is not considered a buy on the markets. But it still supports the buy side because you lockup your steem for a period of time. You basicly 'convert' your STEEM to STEEMpower. This means your STEEM can't be sold to lower the price of STEEM on the markets. (lots of sellers means a lower price if there is not enough buy support to hold the price.)
Now using your SBD is considered a buy. You are putting new capital (Steem dollars) into STEEM. This supports the buy side.
I never bought STEEM with my creditcard I always use bitcoin or Ether. But you can use https://changelly.com/ to buy STEEM with your creditcard. I recommend you buy a small amount to try it, and please never buy more you are willing to lose. Good luck!
sweet! thanks so much for explaining it a bit more for me! :)