You will need to set up a local bank account as soon as possible. There are a number of international banks operating in Vietnam. These include HSBC, ANZ, and Standard Chartered to name a few.
You can withdraw USD and VND over the counter at banks. VND can also be withdrawn from ATM machines around town, however, you cannot withdraw USD from ATMs. It is common to make payments using VISA debit or credit cards at supermarkets, restaurants, and hotels, etc., but cash remains the most common form of payment for goods and services.
It is possible to make international transactions from a local bank account to your account in your home country. Your local bank can provide information on this, including advice on online banking services.