The Knowledge. How to Rebuild our World from Scratch

If the world as we know it ended tomorrow, how would you survive?
A nuclear war, viral pandemic or asteroid strike. The world as we know it has ended. You and the other survivors must start again. What knowledge would you need to start rebuilding civilisation from scratch?
How do you grow food, generate power, prepare medicines, or get metal out of rocks? Could you avert another Dark Ages, or take shortcuts to accelerate redevelopment? Living in the modern world, we have become disconnected from