These campfire-building instructions are courtesy of the Girl Scouts of the USA.
Arrange 3 pieces of kindling in an A shape in a cleared area. Set a handful of tinder near the A's crossbar. Light tinder from underneath; let burn until you have a healthy flame.
Add kindling, tepee-style, over tinder, waiting for each piece to catch before adding a new one. As the fire grows stronger, add fuel, 1 piece at a time, as above.