Either with your ATM card and check balance or go in the bank with all your info and ask them for it. Has to be done with an ATM or in person!
You have four different options to check your balance (depending on the bank you're with). You could:
- go to an ATM machine with your card and check the balance, as Rooster said
- call the bank and ask them to let you know (be prepared to answer a lot of security questions though)
- go to the bank personally and ask them there
- go to your online bank account (if you have one) enter your details (personal ID and password) and check it from there