I have an assignment due in a couple of days but I don't know which is what
How do you tell what words are masculine or femimine?
You can't. Period. If you don't know the word at all, depending on the ending you have different probabilities. Words ending in -o are 99% masculine, as there are only a tiny handful of words that are not. A notable exception is "mano", which is feminine. Words ending in -or are also masculine except for four of them. Words ending in -a are not that reliable, as there are quite a few masculine ones with this ending, and quite a lot that can take either gender. Practically all words ending in -ión are feminine. There are many other thumb rules, but inevitably, there are words that simply have to be memorized.
Try looking here: http://www.spanishdict.com/answers/100009/nouns-gender