wood timber stone etc
Castles are made out of cement and/or brick
Castle
you could also use straw and cocktail sticks for the houses and the bridge.
you should use it on a moat
Bricks
Cake.
they use candles.
hammer
You could build it or use Tale of Kingdoms or Castle Defenders mod
Go to the seashore and build a sand castle. Then try to build a water castle and/or an air castle. That should tell you everything you need to know to answer this question.
Yes, it was used to build stuff.
hammer,nails,and saw