Metal layer of a shield cover prevents RF radiation by "swallowing" it using eddy currents. The lower the RF frequency, the thicker the shield wall must be. The penetration depth depends on conductivity and frequency. At low frequencies, also magnetic effects can be prevented by a shield, then , in addition to conductive metals, also high-permeability metals are used. Again, the lower the frequency, the thicker the wall must be.
360-degree shield prevents radiation to all directions in 2D. Any gap or opening does radiate and must be treated accordingly.