The most obvious difference between stars and planets are size and brightness. Stars are actually suns immense distances away from our location giving the appearance of a point of light in our night sky. Planets are actually satellites of a parent star.
The Sun, our Sun which heats our world and provides our light is nothing less than a nuclear reactor. A middle aged star its core is a healthy 15 million degrees C. (27 million degrees F.) at a pressure 340 billion times Earth at sea level. Such pressures cause the hydrogen in the core to react to other hydrogen atoms to fuse together forming a helium atom. An alpha particle is created from the fusion and expelled from the helium atom as energy working its way to the surface as light. The journey to the surface will take a million years. The surface of the Sun is called the photosphere. The surface temperature is a cool 6000 degrees C. (11,000 degrees F.) and appears mottled due to energy eruptions. Black spots form on the photosphere and are thought to be storms though about a thousand degrees cooler than the area around it. Finally is the chromosphere the area over the surface. Energy passes through the chromosphere as hot hydrogen gas, slower moving particles, light and heat and the whole spectrum of radiations are expelled from the Sun into surrounding space. The outer area of the chromosphere is called the corona. The corona is what is visible during a total eclipse.
Planets, Earth being one, are satellites to a parent sun. Planets are thought to have formed from the materials from the sun as it was forming. Planets are much smaller than their sun. One and one third million Earth’s would fit into our Sun. At a distance of (93 million miles), Earth still receives a very lethal dose of radiation from the Sun. Earth is protected from most of this radiation by its magnetic field. Radiation is deflected around the Earth and only revealed at the poles as the Aurora Borealis. Life has adapted to live on Earth within these conditions.
Other planets share our Sun in our solar system. They are unlike Earth in that no life has been found on those we can reach. They are alike in that they have mass, gravity and some even atmospheres. Other planets have been found circling other suns far from us.