You can use this resource to find out the gender of a Russian noun.
Russian nouns are divided into masculine, feminine and neuter forms. As a very general rule, the grammatical gender of animate objects is decided by the gender, although there are animate neutral nouns such as "animal" (животное) and "child" (ребенок).
Most inanimate nouns are masculine and feminine. The gender of these nouns is largely inexplicable and conditional on various factors (e.g. the root word).
You can establish the gender of most Russian nouns from the last letter of the nominative singular form. These rules are general and by no means definitive. However the general rule states that: usually masculine nouns end in a consonant or the letter "й", feminine nouns end in "а" or "я" and neuter nouns end in "o", "e" or "ë".
But there are many Russian nouns that don't follow these rules. If you want an easy way to find out the gender of a Russian word, use this app to tell you!