There is no difference in meaning; they are both forms of the past tense of "learn". The difference arises in that there is a tendency in British English whereby lots of -ed verbs change to -t, this happened due to pronunciation changes in the past few hundred years. Both are valid and make sense though. learn, learned, learnt burnt, burned, burnt spell, spelled, spelt (spoken only)

The word 'learned' is sometimes used as an adjective, which is used to describe someone who is very well educated or has a lot of formal training. However, it is pronounced differently from the past tense verb. Here are two examples of the word being used that illustrate it's two meanings: "When I was in college, I learned a lot about art history" and then there is "The professor is a very learned man". In the second sentence, where the word is an adjective, it is pronounced with two sylablles. Unfortunately I cannot write it in portugese phonetics for you but in english it might be written "learnid" if written phonetically. I hope this wasn't confusing.