Hey Becky! A short explanation based on most common use. Not considering all definitions you can find looking up on a dictionary, but only common speech. Perceber - understand "Aperceber- se" - being aware or realizing something. To acknowledge or note something you didn't until a given moment. An example about this exact situation: Tu consegues perceber português mas quando estás a estudar português apercebes-te das diferenças entre o português do Brasil e o português de Portugal!