Conductance is the extrinsic property while conductivity is the intrinsic property. This means that conductance is the property of an object dependent of its amount/mass or physical shape and size, while conductivity is the inherent property of the material that makes up the object. No matter how the object changes in terms of shape/size/mass, as long as it is made of the same material and the temperature remains the same, its conductivity does not change. Conversely, the conductance of a conductor changes with its cross-sectional area and length. Of course, a higher conductivity also gives an object a higher conductance. The formula that relates conductivity with conductance is:
$$G=\sigma \frac A l$$
where $G$ is the conductance, $σ$ the conductivity, $A$ the cross-sectional area perpendicular to the direction of electric current, and $l$ the length of the conductor. This formula applies for any (geometrically) prismic or cylindrical conductor, including cuboids.