THE SUN'S CORE
There is a core to the Sun as there are in planets. Stars are different because most of that central mass is made of tons and tons of hydrogen (H) and helium (He). The hydrogen is constantly involved in the fusion reactions, which produce extreme amounts of energy (light, heat, radio waves). Did you know that our Sun used to be hotter? Astronomers now classify it as a G2 star. It is middle-aged and starting to cool and die. Don't worry. It's going to take millions of years for it to burn out. For example, a G5 star is very old and close to death.LAYERS OF MATERIALS
The Sun has different layers in its atmosphere, just like the Earth. Don't get excited, you aren't going to be able to breathe on the Sun. The layers of the atmosphere are huge, swirling masses of plasma at extremely high temperatures. Surrounding the core is a radiative level of plasma. Reactions happen in that layer and churn/stir the next layer, the convective layer. Large amounts of interaction occur in the convective layer. It's constantly spinning the way storms spin on Earth. The outer layer of the Sun's atmosphere is the photosphere. When scientists use special telescopes to look at the Sun, this is the layer they can see.THE SUN'S INFLUENCE
Everything on Earth is affected by the Sun. The Earth's orientation to the Sun creates the seasons of the year. When your hemisphere of Earth is directed away from the Sun, it is winter. When your hemisphere is pointed closer to the Sun, it is summer. So when you're in the Northern Hemisphere and it's summer, kids in Australia might be skiing. As you learn more about the other planets in the Solar System, you will discover that the same idea works for most of them.The Sun's energy is spread around the planet, but is focused on or near the equator. That centerline of the planet is where you will find long sunny days, very little seasonal change, and the warmest ocean waters. From the equatorial regions, energy moves north and south as it circulates around the planet. That circulation can happen in the atmosphere or the oceans.
If you remember anything about Mercury, remember that it is the closest planet to the Sun and really hot. Temperatures on Mercury get up to 460 degrees Celsius. An average temperature on Earth is about 15 degrees Celsius (although it has a wide range). The Sun beats down on little Mercury all day long. 
The second planet away from the Sun is called Venus. It's ironic that Venus is named after the Roman goddess of love and beauty. Venus is one of the harshest planets in the Solar System. It's over 460 degrees Celsius. It has clouds of sulfuric acid in an atmosphere of carbon dioxide. Lava is found across the surface after being spewed from volcanoes. While a harsh place for you, scientists think it's an amazing planet. 
The third planet from the Sun is your home. The Earth is the only known planet where life can survive. As far as we know, there is no other planet in the universe like Earth. We have a very narrow temperature range that allows water to remain a liquid. Life has developed over millions of years because of that liquid. What else makes us special? Most of our atmosphere is made of nitrogen (N), a relatively inert gas. If we had clouds of sulfuric acid or methane (like other planets), life may have never developed. 
Mars is the fourth planet from the Sun. It is a very active planet like the Earth. It has evidence of volcanoes, plate tectonics, and liquid water (as opposed to ice) on the planet. It even has polar ice caps like the Earth, with water in the north and solid carbon dioxide in the south. With all of these similarities, Mars is still nothing like Earth. It only has 40% of our gravity because the mass of the planet is so much smaller. Also, its atmosphere is made up of carbon dioxide and has less than 1% of the atmospheric pressure of Earth.
Jupiter is the largest planet in our Solar System. Its mass is over 300 times the mass of the Earth. If you look at its atmosphere and over 20 moons, you could say that Jupiter is almost like another Sun. There is only one thing missing -- Heat. There is a magical time in a star's life when nuclear reactions start and the star begins to burn. Jupiter never got to that point. 
Saturn is the other big planet in our Solar System. You will find its orbit just outside of Jupiter in the sixth position. It is a gaseous planet like Jupiter and those gases give Saturn a very low density. The big astronomy joke is that if you could find a lake big enough and put Saturn in the water, it would float. Its density makes it lighter than water. While knowing Saturn's density is a fun fact, we know that the thing you will remember is that Saturn is the planet with the big rings. While other planets in our Solar System have rings, Saturn's can be seen from Earth. The Cassini spacecraft is studying the moons and rings of Saturn for several years.
The seventh planet from the Sun is Uranus. William Hershel discovered it in 1781. It is one of the four gas giants in our Solar System, but is much smaller than both Jupiter and Saturn. You will find that Uranus is similar in some ways to Neptune, the eighth planet. Only one Voyager probe has flown by Uranus so very little is known about the planet. 
Neptune is the eighth planet form the Sun. It wasn't discovered until 1846. It wasn't even actually seen with a telescope for several years after that. Astronomers noticed some funny movements in the orbit of Uranus. The changes in the expected orbit were so large than they decided another planet must exist. They made the calculations, looked in the right place, and found Neptune. 
We didn't even know that Pluto existed until the 1930's. Astronomers studied the orbit of other planets in the area and noticed a little wobble. The wobble was big enough for astronomers to start looking for a source. Eventually Clyde Tombaugh found Pluto. In recent years, additional large bodies have been discovered just beyond Pluto's orbit.