How can I make the shields(how to use log)?

And what is crystal?

I'm not good at English. Please say to me easily.

well, you put the log over the crafting table that is outside of the shop, that should show you a menu where you can see the different types of shields that you can make, and the crystals....as far as I know they only been use to summon some kind of dark entity which I don't know for what purpose is this entity used...