Companies and ETFs will sometimes pay dividends to shareholders when they make a profit. These will usually be shared back to shareholders at different times during the year. What you decide to do with your dividends is entirely up to you.
Once its been applied to your Wallet balance, you have the option of withdrawing it, using it to buy other shares or reinvesting the money.
If you would like the dividends you receive from your investments to be reinvested you will need to set this up directly with the share registry your shares are registered with.
The main two share registries are MUFG (formerly Link Market Services) and Computershare.
To access the share registries you will usually need your HIN which can be found by logging into your account, clicking your name in the top right corner and navigating to Account Settings.
Details about dividend reinvestment will also be sent to you by the company or ETF when you first buy your shares.
Please note that there may be tax implications for Dividend Reinvestment Plans and you may wish to seek tax advice from a professional.