Instructions
Wander around the surface until you find sand. It's most abundant near bodies of water.
Left-click on the sand to harvest it. If you have a shovel, you'll harvest it faster, though you can do the work by hand.
Attack and kill monsters when they emerge at night. Periodically, they drop sulfur. Pick it up.
Right-click on your workbench. This summons the crafting grid. Place sulfur in the middle square, as well as in each of the corner squares. Fill out the rest of the grid with sand. This creates C4.
Drop the C4 and hit it once. It will begin blinking. Within two to three seconds, it will explode. Run for cover.