In Costa Rica you'll find that most ATMs ("cajero automático") have a fix withdrawing fee for international cards like Visa/Mastercard. ATMs that have fees are legally obliged to display a screen that indicates the exact amount and ask a confirmation. So feel free to test around, and cancel the transaction if the fee is too high for you.
The currency in Costa Rica is the Costa Rican colón (code CRC, symbol ₡). 1 US Dollar is roughly equal to 600 CRC.
Your own bank may also add its own fees. This is specific for each bank, so check with your bank pricing to see the fees for international withdrawals.
ATMs have both a per-withdrawal and per-day limit which goes from around ₡100.000/withdrawal to ₡250.000/withdrawal and ₡100.000/day to ₡500.000/day. Usually, the higher the withdrawal fee the higher the limits.
Almost all ATMs in Costa Rica are available in English and are also able to dispense USD.
Don't forget to ask for a receipt, especially when you're abroad. And once you have it, take a picture of it immediately because you'll probably end up losing the paper. Make sure the amount on the receipt matches the amount on your account. And in the case of a dispute, use your receipt/picture as a proof.