The message will typically ask you (usually with a sense of urgency) to click on a link to a website or call a phone number in order to verify, update or reactivate your account.
The website link will lead to a bogus website and the phone number to a fraudster pretending to be from the legitimate company. The goal is to get you to disclose any information that can then help the fraudsters steal your money.
This image is a concrete example of smishing. The link and destination address are very often the first elements that will allow you to detect fraud. Other indicators may also help you to spot the scam.