If those policies are under the syllabus, you should be aware of their meaning as well as their significance in terms of the Cold War. All three of these policies are fairly straightforward and can be defined as follows:
- Containment was a foreign policy that was adopted by the United States which aimed to contain and isolate communism so as to prevent it from spreading and being embraced in neighbouring countries.
- The domino theory is a geopolitical theory that states that an increase or decrease in democracy in one country tends to spread to neighbouring countries in a domino effect. The containment policy is considered to have been based on the domino theory.
- I believe that peaceful coexistence refers to the Soviet Union's perspective, which was that itself and the US could coexist instead of being in conflict with each other. There were diplomatic initiatives from USSR officials to demonstrate the USSR's commitment to this idea.
While I did not take Modern History, it appears that you need to be aware of each of these policies as they constitute a significant part of the "Development of the Cold War to 1968" syllabus dot point as you may be required to discuss them in your Section III response, i.e. there is a chance that these policies may be tested in the HSC exam, which is the reason that it is important to be familiar with them and their relevance to the topic as a whole.
I hope this helps!