How do you identify metre in poetry?

Identifying metre can be tricky, since it is sometime quite subtle. However, the easiest way to find the metre is to read the text out loud, placing additional emphasis wherever it feels natural. This will usually give you some idea of the pattern. You can also tap your finger to the rhythm of your speech, if this helps you. Noting the pattern down on the text with symbols for stressed and unstressed syllables is useful for keeping track. If you really don't understand metre, then it's better not to talk about it. Examiners won't mark you down for not talking about something and there will always be other things to talk about. If you do mention it in an answer, it should always be for a reason, and not just to show that you know what it is.