right click with nothing in your hand
You use fire
Right click it using flint and steel, or use redstone to detonate it from a safe distance
If you mean classic (Which I think you do) It wasn't made to explode (as is: It can't)
On Minecraft Pocket Edition, it is impossible to detonate TNT in creative mode. In survival mode, you have to obtain a flint (from mining gravel) and iron (from iron ore) and create flint and steel. You then have to create the TNT and lay it down. Then just tap the TNT with the flint and steel.
Okay, first off you need to get TNT then, you can detonate it witheither a lever, flint & steel, pressure plate, and more. Then it blows up and... its awesome.
The new 1.7 update changes the TNT so that hitting it does not activate it anymore. You need to place a button / lever / redstone torch next to it to detonate it now.
Its free
The ID (code) for TNT in Minecraft is 46.
Yes
Only on mondays
You can set TNT off in Minecraft Beta by clicking it, or by triggering it with redstone.
The number ID for TNT is; 46.