What is the difference between Buying Power and Available Cash (Robinhood)

For context I got a bonus from Robinhood which I forgot to account was for how much worth of shares exactly but after investing for 25.95$, I got 29.84$ despite making a negative return on Mastercard (21$ of my investment) and a VERY SMALL positive return on BTC (bought for 4.95 and got 5.56$) at the end. So anybody mind explaining it to me please?