You may have corrupted the world by using mods or other unlisenced programs to edit the game. It is best to revert to a backup that you have saved before.
because you are in adventure mode
You can. Your computer is wrong.
In Minecraft, you place any type of block by right clicking. Simple as that. This includes Dirt blocks.
You can always break and build any thing u want in creative. If you are in "adventurer mode" that stops you from braking and placing blocks.
You build buildings on minecraft the same way you build any other structure. First, gather the materials you need. Then, select the material you want to use for building and right click on a place on the ground to place a block. Place the blocks in the shape of a building, and you're done.
So far i cant find any :(
You type a command into them, then activate it like any other redstone item
On PC, it is infinite (or until Minecraft runs out of memory).
The two main methods of placing multiple blocks at the same time in vanilla Minecraft are either: Fill Command, type "/fill x y z x2 y2 z2 block" replacing x,y,z with the start locations and x2,y2,z2 with the end location (making a rectangle area). The block should be replaced with any of the Minecraft blocks for example 'stone'. This requires command blocks unless you want to type the command each time and relative coordinates can be used.
In theory any size, but in practice about 8 million blocks square and 200 high.
place it like any other normal block
Minecraft blocks don't have any material value, but their dimensions are around 4cm*4cm*4cm. A fully generated Minecraft world would have a larger size than Neptune.
place a 3 by 3 square of tnt and replace the middle one with water. add another ring of any block around the tnt. Place redstone on top of that ring of blocks. To launch, stand in the water and power the redstone.