There's currently no way.
They should have updated it by now to have the Flint and steel
I assume you mean TNT. All you have to do is hit it.
tap the tnt with flint and steel
In the next update.
If you mean classic (Which I think you do) It wasn't made to explode (as is: It can't)
you can with different of stuff eg: lava, fire charge like those thing. You can redstone power to set off a TNT
You cant
TNT can be ignited by using a Flint and Steel on it, or providing charge via a switch (lever, pressure plate, etc) or by an active redstone current.
you can't ):
The previous way to explode TNT was by punching it. However, you can also make the TNT explode by placing it near lava (a timely manner to explode it), clicking on it with flint and steel, or any contact with fire. If you were not in classic, it could also be ignited by Redstone or fire charge or even a fire arrow (assuming you have the latest version of Minecraft). In the related links below, I have listed the wiki article for TNT.
If TNT explodes while in water it will not destroy blocks but will damage any mobs (players, animal or monsters) in the blast radius.
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.