The concept of fields is the concept of assigning numbers to every instance of time and to every point in space. Think of temperature. You can assign a temperature value to every point in space whenever you like by going there and measuring the temperature with your favourite temperature probe. Now consider another field: wind speed. This is a vector field, i.e. it consits of 3 numbers corresponding to direction and magnitude. Clearly, both fields interact since wind can carry away heat energy or transport colder air to a given place. You can now start to reason about whether or not the temperature and wind fields are real or in fact made up by different entities like particles (or again fields). What is irrefutable is the description of a physical phenomenon, wind and temperature, and their interactions. Whether this is the most fundamental one, you can never know.

The concept of fields is the concept of assigning numbers to every instance of time and to every point in space. Think of temperature. You can assign a temperature value to every point in space whenever you like by going there and measuring the temperature with your favourite temperature probe. Now consider another field: wind speed. This is a vector field, i.e. it consists of 3 numbers corresponding to direction and magnitude. Clearly, both fields interact since wind can carry away heat energy or transport colder air to a given place. You can now start to reason about whether or not the temperature and wind fields are real or in fact made up by different entities like particles (or again fields). What is irrefutable is the description of a physical phenomenon, wind and temperature, and their interactions. Whether this is the most fundamental one, you can never know.