Extra Parts is simple enough: it adds extra tool parts for Silent’s Gems. It does not add the materials required for building tools (at least they are not craftable), so you will need other mods installed along with this one. For example, you will be able to make tools from bronze if you have another mod that adds bronze ingots (and properly registers them in the ore dictionary).
The additional materials can of course be mixed in with materials from Silent’s Gems. For example, you could make a tool that’s part metal and part gem. Any combination will work as long as all materials are of the same tier.
This is for Minecraft 1.9+ only. The original version of Silent’s Gems doesn’t allow new materials to be added, so porting this mod to 1.7/1.8 is not possible.