The reconfigurable intelligent surface (RIS) is an emerging technology, which will hopefully bring a new revolution in wireless communications. The RIS technology can be deployed in an indoor/outdoor environment to dynamically manipulate the propagation environment. The RIS consists of a large number of independently controllable passive elements, and these elements are involved in realizing high passive beamforming gain. Different from the conventional active phased antenna array, there is no dedicated radio-frequency (RF) chain installed at the RIS to perform complex signal processing operations. Therefore, it does not incur additional noise while retransmitting the incident wave, which is substantially a unique feature from the conventional wireless communication systems. Taking advantage of its working principle, RIS has been deployed in various practical scenarios. In this tutorial, at first we will review the latest advances in RIS, including the application scenarios such as the system and channel model, the information theoretic analysis, the physical realization and design, key signal processing techniques such as precoding and channel estimation, and prototyping. Finally, we discuss interesting future research problems for the RIS-aided communications.