Metasurfaces, a class of thin metamaterials, have shown unprecedented capabilities in the local manipulation of phase, amplitude and polarization of electromagnetic waves from microwave to optical frequencies by tailoring the geometry of building elements. At microwave frequencies, they are constituted by sub-wavelength size patches or pins printed on thin grounded dielectric substrates or realized as a texture in a metal surface. During this course the background and basic theory of different types of canonical metasurfaces will be explained, as well as how to realize such surfaces for different applications, and how to devise good theoretical models and implement them numerically.