Aside from means except for or besides something. When you say “aside from math, I like all my subjects,” you're saying that math is the one exception: you like everything else. When someone says “aside from pizza, we have sandwiches for lunch,” they're pointing out that pizza isn't the only option.

The phrase works two ways. Sometimes it means excluding something: “Aside from one mistake, you played the piece perfectly” means that if you ignore that single error, the performance was flawless. Other times it means in addition to: “Aside from soccer, she also plays tennis” means soccer isn't her only sport.

You can usually tell which meaning fits by context. If someone says “aside from being tired, how do you feel?” they want to know about everything except your tiredness. But “aside from homework, I need to walk the dog” means you have homework plus another responsibility.

The phrase set aside is related: when you set something aside, you move it out of the way, just like aside from moves a topic out of the main discussion. You might set aside money for a bike, or set aside time for reading. Both uses involve putting something in a separate category from everything else.