Just like we might generally know what honesty is, we might know what facts are. Here are some easy ones.
If I throw an apple up into the air above me, it will come down.
The sun is going to rise tomorrow (even if I cannot see it with my eyes).
If I use some salt water with two different metals connected by a wire, I can make a battery.
Now, the first two facts are pretty easy to understand. The last one is a bit more tricky, especially if you didn’t know that fact. While I don’t want to get into the philosophical rabbit hole of epistemology (the theory of knowledge) right now, it is important to see that facts are very different from what we call opinions.