The Basic Rules state that you can get a possible bonus action. Is this entirely up to the dm or are there circumstances where it is guaranteed? Players handbook doesn't include the bonus action.
The PHB is only talking about getting an additional Action on top of your normal Action and "possible" bonus action.
On your turn you always have access to your Bonus Action. Its just that things that require a bonus action are not that prevalent, so you don't always use it.