In high school, I learned how to understand powers of ten, scaling, exponents, and orders of magnitude. This helped me later in on my engineering career. Even later, when I was saving money for retirement, it helped me understand investing, compound interest, and the "rule of 72" (if money earns 7.2% interest annually, it will approximately double every 72/7.2 = 10 years). It also helped me to understand the world better, because numbers like "a population of 8 billion people" mean more to me than just "a big number."

The most important "skill" I learned from math class is its purpose. Math is about developing logical thinking (unlike language and history, which develop analytical thinking). Students in higher level math classes often ask what the purpose of learning such concepts is, since most careers won't require such high levels of math, but now I have an answer for them.

I learnt to avoid being noticed. When the teacher asked a question, he would never pick on me. This is a fundamental life skill deeper than any mathematics.

A basic function I learned in my math class would be the simple operations of addition and subtraction. When shopping at the grocery store, sometimes we use coupons; using coupons will usually help by providing a discount of the original listed price of an item. Thus, to figure out the difference, subtraction would be an appropriate function to determining the new total after the coupon was applied.