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.
Cardiff Castle is primarily constructed from a combination of local materials, including sandstone and limestone. The castle's medieval core features strong stone walls, while the more ornate Victorian additions, designed by architect William Burges, incorporate decorative elements made from materials like terracotta and cast iron. The use of these materials contributes to the castle's distinctive architectural style and historical significance.
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.