I know 100 is average but I have never really understood how the rest of the scale is structured. Like what is the difference between 85 and 100 in real life and what does it actually mean to score 70 versus 115 versus 130? Is the scale linear so that the difference between 100 and 110 is the same as the difference between 130 and 140 or does it work differently at the extremes?
The scale is linear but what the numbers mean in real life is not evenly distributed. IQ follows a normal bell curve with a mean of 100 and standard deviation of 15. About 68 percent of people fall between 85 and 115, which covers most of humanity and handles most everyday cognitive demands just fine. Below 70 is associated with intellectual disability. Above 130 is the traditional giftedness threshold at roughly the top 2 percent. The practical consequences of score differences are steeper at the lower end of the distribution than the upper end, which most people find surprising.
Here is the humbling part nobody mentions. Most people who think they are a 130 are probably a 115, and most people who think they are a 115 are probably closer to average. The Dunning Kruger effect and the IQ obsessed corners of the internet are basically a perfect storm of overestimation 
Take an actual validated test before you start building your personality around a number you got from a free quiz at 2am.