A solution is a homogeneous mixture involving a solute and a solvent. The solute is the substance that gets dissolved and the solvent is the liquid in which the solute dissolves.
A suspension is a heterogeneous mixture of a liquid and a solid. The solid usually does not dissolve, and can be very visible to the eye. Sometimes the solids are heavy, and large enough for sedimentation (particles settling down in layers) in the container holding it. Unlike colloids, regular agitation is needed to keep mixture fairly mixed.
A colloid (also known as colloidal dispersion) may look like a homogeneous mixture, because the mixture looks very uniform. Under a bit of magnification, the solute is not completely dissolved, and the particles are big enough, making the entire mixture cloudy.