This is the 2174th most frequent Dutch word.
leerde
"Leerde" means "learned" or "taught" in past tense.
Here, 'leerde' is used as the simple past form of the verb 'leren', indicating the action of learning something in the past.
Ik leerde gisteren een nieuwe taal.
I learned a new language yesterday.
In this context, 'leerde' is the simple past tense showing the acquisition of a skill (swimming) during a period in the speaker's youth.
Toen ik jong was, leerde ik zwemmen.
When I was young, I learned to swim.
Here, 'leerde' is used as the simple past tense to refer to the process of learning something, which is being recalled or questioned.