How does a new TV series ensures that its actors will be available for the future? [closed]

As I understand it, a new TV series sometimes goes like this:

1. A pilot episode is produced,
2. the network airs it or test-runs it,
3. and the network decides whether to contract more episodes for a season.
4. Future seasons are then approved based on the performance of past seasons.

If there is slack time between the last production and the approval of more episodes,

1. How does a TV series ensure that its actors will be available for new episodes, while waiting for the network's decision?

2. Are the actors prohibited from taking other work that would make them unavailable for the series?

3. If so, are the actors paid something if the series is terminated, to compensate for their not accepting other work?