What app or site is best?

I'm just trying to order something online and they want crypto if someone could help me 😭 I feel a bit lost staring at everything to many options I just wanna plug my card it convert then send it over to the seller without a bunch of hassle I've done so much research already that I feel kinda lost on how to do this and they take a few different currencys BTC USDT-tron USDT-solana and lastly I guess USDT- Ethereu but I'm assuming BTC is the most common? Wait can cash app convert monies to Bitcoin??