What is a nucleophile?
A nucleophile is most simply defined as an element that donates electrons. Conversely, an electrophile is an element that prefers to accept electrons.
Tips for finding nucleophiles: a nucleophile will ALMOST always have an anionic charge. This is because it has excess electrons that it is capable of donating to an electrophilic atom.
Notice the parallel between Lewis acids and bases:
Lewis acids accept pairs of electrons (making them electrophiles), and Lewis bases donate pairs of electrons (making them nucleophiles). Hope this helps!