To ‘buy’ flexUSD you must ‘mint’ it by following these steps:
1) Deposit USDC to CoinFLEX (learn how to do that here)
2) Go to https://coinflex.com/flexassets
3) Select ‘mint’
4) Enter the amount of USDC you want to exchange for flexUSD
5) Click ‘confirm’ and you’re good to go!