Your question is quite general. A strobe signal is used to stimulate the system at the other side of the interface. In other words strobe signal is used to make the other system start the transmission of incoming/outgoing data.
Strobe signals is kind of self clocking, the time at which data is to be recognized and considered valid. It is used in encoding of data. We can recover clock by XORing of two signal data signal and Strobe signal.