It went something like that, during WWII Russia suffered big losses when attacking Finland and in order to focus their efforts somewhere else Russia proposed a neutrality pack with Finland and other Scandinavian countries (unsure about this part). So Finland become a neutral country in exchange for Russia pulling their military and taking a piece of their land. They want to join NATO because they do not trust Russia to honour their agreement towards them and are seeking a protection kind of thing which all in all is beneficial for NATO countries as it puts even more landmass between core members and Russia. I hope this makes sense and should be accurate enough information for you to look into it further if you are interested.