Brother,
As you said you are not expert, then you should not write such questions like "Do you even know how multigrade oils work?" Because such questions looks like bit offensive to ask someone. No?
Anyway please have a brief look at the following topic and then switch to Multi-grade and read their functionalities.
Motor oil - Wikipedia, the free encyclopedia
Also, the indicated numbers on oils like 5/30, 0/40, 10/30, 15/40, 20/50, etc. shows freezing temperatures in Fahrenheit (FO) and hence viscosities are considered accordingly.
Higher the temp. means high viscose oil (thick) and multigrade refers its performance at difference temperatures.
Cheers.