In French, there are two categories of nouns, feminine and masculine. Most students find it difficult to distinguish between them, as there are many exceptions to the rules and the genders of some nouns seem to be randomly chosen.
The nouns will almost always be associated with the definite article (le or la for singular, les for plural), and this is why, in writing, it's really important to identify what type of noun you are using.
Here are a few tips on how you could easily differentiate between them, based on word ending:
1. Words ending in consonants
The majority of them will be masculine (e.g. l'oeuf - egg, le nord - north, le parfum - perfume, le pain - bread, le mur - wall) but there are certain exceptions that can be learned (e.g. la mer - see, la soif - thirst, la faim - hunger, la fin - end, la main - hand, la voix - voice). The single syllable ones tend to be feminine, whereas the other ones tend to be masculine.
2. Words ending in -e or -ée
These tend to be feminine, excepting the nouns ending in -age, -ege, -é, or -isme. Some examples are: l'année - year, la rue - street, la différence - difference.
3. Words ending in -on
Again, these are specific for feminine nouns. Some exceptions to the rule are: l'avion - airplane, le crayon - pencil, le ballon - balloon or football, all of them being masculine.
However, there is no certain way of determining the gender of every noun that you may encounter (it's sometimes difficult even for native speakers!). Whenever you learn new vocabulary, try to visualize the word you are learning, and use colour-coordinated notes to help you remember. By practicing regularly and making your own set of rules, you will eventually master the French genders.