Free play on Starburst is usually a demo version of the same game, with the same return, the same hit frequency and the same reel set. Nothing is deposited, so nothing can be withdrawn from it. If you move to real money, the published terms of the partner apply: a minimum deposit of US$20, a first deposit bonus of 600% cash, daily cashback of 10% of losses, and a maximum bet of A$5 while a bonus is active.
The A$5 cap is worth reading twice, because it is low relative to the stake sizes many players use. Bonus funds and cashback come with conditions, and cashback is a percentage of losses, not a payment for playing. Check the full terms on the partner's site before depositing, and never treat a bonus as a reason to spend more than you planned.