The three-dimensional (3D) patterns of a metamaterials can be modified into a two-dimensional (2D) pattern at a surface or interface by arranging a set of electrically small multiple elements or apertures. This two-dimensional surface version of a metamaterial has been known as metasurface or metafilm. The 2D metasurface is an alternate option to bulky 3D metamaterials. The metasurface structure requires less physical space in comparison to metamaterials which results in compact size and lower loss. Metasurface can be modeled using effective-medium theory, but the more suitable method to characterize metasurfaces is by their effective surface electrical and magnetic susceptibilities. These surface susceptibilities are correlated to the scatterers that constitute the metasurface. There are various applications of metasurfaces, ranging from microwave to optical frequencies. This overview provides a framework for designing and developing new metasurface antennas to meet the demands of future applications.