So, of course, first get a TNT block. (Also known as TNT).

Then, place it down, (by right clicking.) and then get any of these:

Flint and steel

Fire Charge

You can get any of them, it works in the same way.

After, get one of them and right click the TNT block. It will ignite and wait for 1-5 seconds for it to explode. Now you’re done! But TNT does not work in water.

Remember everyone, you need a crafting table to craft these items. A crafting table looks like this

Right click into the crafting table. You should see this:

The crafting table grid above, is where you use to craft items. While in your inventory, the crafting grid looks like this:

But how do you craft TNT?
Ingredients: 5 Gunpowder 4 Sand

How to craft:

Scroll back up the page, and you will see how to light the TNT.