We tend to learn facts. We do this by studying over a relatively long period of time. After studying them for a period of time, we can usually say that we have learnt them.
When you were a child, you did not know that 2+2=4. You had to study maths. After a while, you learnt that 2+2=4. You studied addition until you understood how to add two numbers together. Once you had studied it and understood it, you knew how to add numbers together.