Instructions
Right-click to place your TNT block, once it is selected from your inventory, on any space in the game. It's impossible to ignite a TNT block placed underwater. Rain also extinguishes the fuse.
Use the Flint and Steel item on the TNT to light the fuse. You have a few seconds before the TNT explodes to retreat to a safe distance.
Use lava, obtained deep underground with a bucket, on the TNT to light it on fire. Do not touch the lava, as it is harmful and can kill your character.