The acronym IRAC stands for a methodology of legal case analysis, regardless of whether we analyse a decision a court already made, or whether we are trying to solve a case. 

The first step is to outline the ISSUE. Gather the facts, tell the story. What happened? Who was involved? What did they want? 

The second step is to identify the RULE(S). This may be easy or complicated depending on the complexity of the case. When dealing with apex courts' cases, this part would often involve PRINCIPLES, value judgments etc.

After knowing what happened, why, who etc. and after knowing which rules would be applicable and why, we can APPLY the rules to the facts. This would involve interpretation of the rules, argumentation, or even discussions regarding different interpretations. 

CONCLUSION presents the results of the above-mentioned process. It can be short (in a shorter case summary) but it can also be a complex analysis and discussion of what happened in the first three steps. It can (and it is welcome) involve scholarly literature, case-law and other relevant sources. 

A very brief explanation of how this particular structure of summarising cases works may be found here (yes, it is Wikipedia :) ) https://en.wikipedia.org/wiki/IRAC