Many stars belong to close binary or multiple stellar systems. Moreover, since 1995, a large number of extrasolar planetary systems have been discovered where planets can orbit very close to their host star. Finally, our own Solar system is the seat of many interactions between the Sun, the planets, and their natural satellites. Therefore, in such astrophysical systems, tidal interactions are one of the key mechanisms that must be studied to understand the celestial bodies' dynamics and evolution. Indeed, tides generate displacements and flows in stellar and planetary interiors. The associated kinetic energy is then dissipated into heat because of internal friction processes. This leads to secular evolution of orbits and of spins with characteristic time-scales that are intrinsically related to the properties of dissipative mechanisms, the latter depending both on the internal structure of the studied bodies and on the tidal frequency. This lecture is thus aimed to recall the basics of the tidal dynamics and to describe the different tidal flows or displacements that can be excited by a perturber, the conversion of their kinetic energy into heat, the related exchanges of angular momentum, and the consequences for astrophysical systems evolution.