The Copper Block is bulk storage for your Copper Ingots. It can also be used as an attractive and unusual looking decorative block.
It can be crafted out of 9 Copper Ingots from Galacticraft. If you have another mod installed with a different variety of copper normally you can mix and match the ingots to craft a Copper Block.
(In GC3 only) a Galacticraft Copper Block will be made from mixed copper ingots if you use at least 1 Galacticraft Copper Ingot in the recipe - but if you use zero Galacticraft ingots then a Galacticraft block will not be made. This recipe requirement for minimum 1 Galacticraft ingot allows you to control whether the Copper Block from Galacticraft is made or the copper block from the other mod.