perlocutionary acts are the third aspect of speech acts classified by Jl Austin. perlocutionary acts are not an integral part of the act itself performed by the speaker but rather refers to impression made on the listener. In other words, perlocutionary acts are the affect achieved by the speech act. For example, when someone says “it is raining” the perlocutionary part of the utterance will manifest itself if following that proclamation someone takes an umbrella with him.
To give another example sentence: in “don’t do that!” locutionary act is the meaning of the words, the illocutionary act is the attempt to warn someone and the perlocutionary act is that someone no doing that.
In order to give good examples of perlocutionary acts just think of the way an utterance affects someone. It is not the message denoted (locutionary), not the message conveyed (illocutionary) but the message as having some sort of impact on the receiver.