This image is actually the best way to show one what exactly the Drake equation is and what it predicts. Many people get the wrong idea and assume that it is a reasonable person's way to show the existence of aliens but that really isn't it at all. It is really just the best possible way we have to accurately deduce the probability and likelihood of there being an advanced civilization out there beyond where our little eyes can see. It takes into account the vast amount of stars, solars systems, galaxies and also specific planets that are likely to be at a good distance from their parent star. This distance is important because the distance between a planet and it stars plays a huge part in many things that would make it a habitable planet or not for our brand of life or any other life loosely based on carbon.
It's really a pretty elementary cosmological idea that; the closer you are to a star.. guess what.. the warmer you are! yeah. So obviously Earth is at a perfect point for our type of life to exist, therefore when we make assumptions based on the Drake Equation we look for planets that are roughly the distance that WE have from our star. We also look to see the mass of the planet because this will have an affect on the gravity. Our gravity is perfect for our type of life, if we lived on a more massive planet we would be crushed by our own weight and vice versa if the planet was less massive. Some theorize that if there were intelligent life out there on a more massive planet, then they would likely be very low to the ground and have very stout, strong, structural bones and what not. I think this is a pretty common sense assumption but it is very thought provoking and interesting.
All of this is also considering that our brand of life is likely the only type to exist. There may be chlorine based or methane based life out there.. we just don't know because our laws of physics could be completely different for a different galaxy or a different solar system.. We just don't know yet... Which is why we need to fucking look US government!!!
All of this really just sounds like an equation that puts us back where we were in a way.. We still don't know.. Here is Chad Brown's "in a nutshell" of what the Drake Equation means to us:
There are a shit ton of stars, therefore there are probably a shit ton of planets, this in turn increases the likelihood that there are probably planets out there that could be habitable to life like ours.
It's a pretty reasonable assumption when you consider the numbers involved. There are approximately 1,000,000,000 stars in our galaxy. Yeah. Our sun is ONE of them. Humans can't even accurately comprehend numbers that large. 1 Billion seconds equals over 3 years. Think about that to make sense of the biggness of that number.
I honestly have no idea why I rambled about the Drake Equation because I am not a scientist and I honestly don't know exactly how to feel about the data it predicts, but I find it interesting and there is a lot of back and forth in the science community on how we should interpret the data we can get from it and how we should treat it.
It's all up for discussion as it is quit theoretical. I find it interesting.