A Will is a document setting out how you wish your assets to be distributed after your death. Originally the document that was used to distribute your personal property(clothing, furniture, and money) was known as a Testament, and the document disposing of real property (House and land) was known as a Will. Overtime both of these documents have been combined and are known as a Last Will & Testament that disposes of both real and personal property.
In Australia today most people own a car, furniture, bank accounts, perhaps a property and shares, and other inheritances. When you make a Will you direct who will be the executor of your Estate, which family members or friends will receive your possessions following your death, and if you have children who will be their guardians.
If you die without a valid Will your estate may be divided according to the laws of intestacy leaving your estate to people you may not even know.