What needs to happen before you can use the reason cpctc

You need to determine whether the triangles are congruent by ASA, SSS, SAS, AAS or HL. Then you can say that the triangles are congruent; after that, you need to go back to what the were asking you to prove, for example, if they were asking you to confirm that AC and GD were congruent, state that they are congruent and then put CPCTC as a reason. Am I making sense?