- Steam is hot in temperature
- A hot substance is a source of heat
- Therefore, steam is a source of heat

- Cooking food requires adding heat energy to the food
- A source of heat can be used to heat something
- Hence, a source of heat can be used to cook food by adding heat energy to the food

- Steam is a source of heat
- A source of heat can be used to cook food by adding heat energy to the food
- Therefore, steam can be used to cook food by adding heat to the food

- Steam can be used to cook food by adding heat to the food
- Adding heat to something means trasferring heat to that something
- Hence, steam can be used to cook food by transferring heat to the food

So, steam can be used to cook food by transferring heat to the food
Q: Why can steam be used to cook food?
Context:
- Adding heat to something means trasferring heat to that something 
- Steam is hot in temperature 
- A hot substance is a source of heat 
- Cooking food requires adding heat energy to the food 
- A source of heat can be used to heat something