What is the difference between The Magnetosphere and Earth's magnetic field?

The Magnetosphere and Earth's magnetic field are related, but they are not the same entity.

Earth's magnetic field surrounds the planet and is generated by the motion of molten iron in the Earth's core. It is a three-dimensional field that has both a magnitude and a direction at every point in space. The strength of the magnetic field varies at different points on the surface of the planet, and is typically measured in units of gauss or tesla.

Earth's Magnetosphere, on the other hand, is the region around the planet that is influenced by the Earth's magnetic field. It extends from the upper atmosphere into space, and is shaped by the interaction between the Earth's magnetic field and the solar wind, a stream of charged particles that flows out from the Sun. The magnetosphere acts as a protective shield, deflecting much of the solar wind and protecting the planet from harmful radiation.

In other words, the Earth's magnetic field is the source of the Magnetosphere, but the Magnetosphere is a distinct region that is created by the interaction between the magnetic field and the solar wind.

This page is referenced from here. Knowledge of the magnetosphere and its relation to the Earth's magnetic field is important to understand the role of geomagnetic activity on HF propagation conditions..