There will be a total eclipse of the Sun on August 21, 2017. A total solar eclipse occurs whenever the Earth, the Moon and the Sun line up in that order. By being in the middle, the Moon casts its shadow upon the Earth.
You would think that since the Moon travels around the Earth about once per month, we should have a solar eclipse every month. Well as you no doubt know, we do not have monthly solar eclipses.
Here are the Earth, the Moon and the Sun drawn to scale in terms of size and distance. (Actually, the one length that could not be drawn to scale is the Earth-Sun distance. To be to scale, the Sun would have to be placed at about 40 feet (about 12 meters) to the right of where it is on your screen.)

Now for the explanation why solar eclipses do not happen very often. The Moon does not orbit the Earth on the same plane that the Earth and the Sun are on. The Moon’s orbital tilt is about 5.15° from the Earth Sun plane. If you look very carefully at the left side of the screen you will see the letters ‘A’ and ‘B’ indicating the position of the Moon’s maximum orbital tilt. So, at every New Moon, the Moon could be absolutely level with the Earth and Sun (as it will be on August 21, 2017) or it could have an orbital altitude as high or as low as 5.15° and its shadow will miss the Earth entirely.

Perhaps you’d like to make your own solar eclipse diagram, drawn to scale like the one above. (Heck, it might even make a good science project, if you need one).

Using the statistics below would be difficult to show in a classroom, but you could reduce the size of all these figures.
OR you could state (while holding a 1.5 inch Earth model 3.65 feet away from a .4 inch Moon model) that the Sun would be a 13 foot sphere placed about a quarter of a mile away!!
Now you know why the diagrams in science books are not drawn to scale!