It is also a story about family relations. The book showcases a family of six that has to start all over without the basic amenities that make life easier in the eyes of society. The idea of being in an island with no human neighbors is daunting to say the least.
The family was shipwrecked and everyone else on the ship perished when they deserted the ship. When the storm finally abated, they figured out a way to shore and immediately tackled the most urgent needs like food and shelter for the night.
The senior Robinson and Franz, the eldest son, explored the island and found that it was well endowed with food and animals that could be killed for meat. On further exploration, they discovered better shelter and even a salt supply. They had supplies and even wax from which they made candles. They made many more amazing discoveries and got quite comfortable on the island which was hither to uninhabited.