The trick is to not use blocks that are affected by gravity. Sand and gravel are affected by gravity, and will fall in. So use dirt, wood, or stone. Then you will have a perfectly solid structure :)
You can place blocks but not make them.
Without mods, you need to make your world creative mode, not survival.
To make blocks destructible u have to be an op of the server
4 clay blocks i think
No
You make Glowstone Blocks with 4x Glowstone Dust in a square formation, on your crafting grid.
No, you can only place and destroy blocks.
punch/dig clay blocks
You can make blocks out of it, for building with, it can also be used as a dye.
You put 6 blocks of glass in the bottom 6 blocks of your crafting table.
14 blocks of obsidian in a block formation
Just water source blocks.