In the next update.
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.
You cant
you can't ):
By crafting 4 sand and 5 gunpowder with a crafting table
right click with nothing in your hand
They should have updated it by now to have the Flint and steel
Right click it using flint and steel, or use redstone to detonate it from a safe distance
tap the tnt with flint and steel
There's currently no way.
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.