"Opimme toisiltamme" is "we learn from each other".
The words 'each other' do not always look the same, unfortunately. For example, the sentence 'we look at each other' would be translated to 'katsomme toisiamme'. Additionally, "we don't talk to each other" would be "emme puhu toisillemme".
The Finnish equivalent of 'each other' changes based on the verb that precedes it. I'm afraid I don't have a more specific grammar rule at hand, but I hope this helps a little.