This is what ignites the TNT (AKA firework)
Preview picture. Finished firework lighter.
1. Put a block on any of the inside corners like so.
2. Put a block on the floating block opposite of the block you just placed.
3. Put three blocks onto the back of the block you just placed like so.
4. Put 4 blocks on each side of what you made in 2 and 3.
5. Put blocks on the outside of what you made in 4, but don't put one on top of the one you placed in step 2.
6. Place a sign on the side of the block you placed in 2 like so.
7. Where you going to be placing the lava.
8. The sign should stop the lava.
9. Finished product.