This is the 1503rd most frequent Swedish word.
lärt
"Lärt" means "learned" or "taught" in English.
Here, 'lärt' is the past participle of the verb 'lära', used as part of the present perfect tense 'har lärt'. It is associated with the reflexive pronoun 'sig' (himself) to indicate learning a skill.
Han har lärt sig spela gitarr.
He has learned to play the guitar.
In this sentence, 'lärt' is again the past participle, now part of a pluperfect tense 'hade lärt'. It expresses a completed action in the past that relates to a wish or hypothetical situation.
Jag önskar att jag hade lärt mig det tidigare.
I wish I had learned it earlier.
Here, 'lärt' is used in a causative sense, meaning 'taught', and is the past participle in the present perfect tense 'har lärt'. It shows the action of teaching others.