The range of your voice is determined by the highest and lowest notes you can sing. Although everybody has a different voice range, there are some general categories used to describe typical ranges. In traditional four part vocal arrangements, voices are broken up into four categories: soprano (highest female voice), alto (lower female voice), tenor (higher male voice) and bass (lowest male voice). In other arrangements there may be six categories. The female voices are then categorized as soprano (highest), mezzo soprano (a little lower) and alto or contralto (lowest). The three male voice types are tenor, baritone and bass. The middle voices (mezzo soprano and baritone) are the most common voices. Another unusual voice type is the male alto. All of these voice types are descriptions of adult voices. Children and teenagers have voices which are not fully developed, so they cannot be classified as a final voice type.
It is a good idea to determine your range as soon as you understand how to find the notes on a keyboard. However, it is unwise to classify yourself immediately as any particular voice type. It is always best to consult a singing teacher and work with them for a while before classifying a voice. Young students may not be able to classify their voice type until they are adults. The most important thing is to know your individual note range and work with it, rather than straining against it to sing higher or lower than is practical for you.