Laura Bennett
How you tell if a German word (i.e. specifically a noun) is masculine or feminine (or a 3rd option: neuter) is a matter of recognizing various noun endings and noun groups that are associated with one gender over the other two.
Rather than attempting to memorize a seemingly random der, die, or das paired with each German noun (there are thousands!!), memorizing a much much shorter list of noun endings and noun groups will be more effective and infinitely less frustrating.