Without a will,
the law decides.
With one, you do.
Here's an example will, written from three answers.
Example will
Will of Amelia Murray
1.I, Amelia Murray, of Geelong, Victoria, revoke all my earlier wills.
2.I appoint my sister, Kate Lawson, as guardian of my children.
3.I appoint my partner, Sam Murray, as executor of my will.
4.I give the rest of my estate to Sam. If Sam dies before me, it goes to my children in equal shares.

