The unit of currency in Malaysia is the Malaysian Ringgit, abbreviated as RM.
The plural for the Malaysian Ringgit is also Ringgit (not Ringgits).
It is quite common among locals to refer to their local currency as dollars so make sure that you know which dollar someone is referring to.
The best way to pay for large items in Malaysia is with your U.S. credit card; you’ll get the best exchange rate that way. Try to use a US credit card that does not impose a foreign transaction fee when you use it overseas. Capital One and Chase both offer cards that don’t impose foreign transaction fees; many other banks do as well.
Many smaller establishments (food stalls, taxis etc.) won’t accept credit cards, so you will need to have some cash with you most of the time. The best way to get cash is to withdraw it from your US bank account using your ATM or debit card. ATMs are plentiful in Malaysia and just about all of them accept foreign debit cards.