One dollar equals 100 pennies. Three with no fraction would be written 3.0. In the United States, many purchases are made by personal check or credit card. There are several banks in the area, and many will require a Social Security Number before you can open a bank account.
Some banks also charge a fee for their services.
Here on this campus we have Crestar Bank which is located in the Stamp Union. The bank allows international students to open accounts with their UM Student ID number. Give the bank your Social Security Number as soon as you receive your Social Security Card. However, it can be difficult for international students to obtain credit cards. There are strict regulations concerning work permission for foreign students on F and J visas.