You usually set up the USART receiver with the correct (if known) baud rate, stop bits etc. as what the transmitter is using to transmit the data.
Baud rate detection refers to the process by which a receiving device (such as a USART) determines the speed, code level, and stop bits of incoming data by examining the first character, usually a preselected sign-on character (also called a "syncword").
It allows the receiving USART to accept data from a variety of transmitting devices operating at different speeds without needing to establish the data rates in advance.
You will need to set up your processor's baud rate generation block (USART Parameter Registers) before you can transmit from it?