Hello, welcome to the community. You may find these bits of info helpful:
You can use your card while abroad to pay in USD, Monzo will not add a fee on top of the MasterCard exchange rate. Just make sure to always pay in USD and not in GBP as the merchant’s conversion rate will almost always be worse.
You can also withdraw cash in a similar way up to your cash withdrawal allowance which you can see in app – Monzo won’t charge you for this (but the dispensing ATM may) unless you reach your withdrawal limit after which it’s 3% charge I believe