According to Austin (1962) in his speech acts theory, there are three actions related to speech acts. The first act is locutionary act which is the basic production of meaningful utterance. This act is much related to the hearer, if the hearer fails to understand what the speaker is saying then the speaker has failed to do a locutionary act . For example, when a person from Indonesia (he's in America for instance) talks to an American in bahasa 'apa kabar pak?' in English this utterance will not produce what is called as a meaningful linguistic expression. On the contrary when the speaker said 'how are you sir?' then the American would understand and it is a form of locutionary act. (see more simple examples of locutionary acts)
In uttering a sentence or word, one must have a certain intention. Most of the time people produce well-formed utterances for a purpose, for instance the need to communicate something to someone or to provide facts. This second dimension is called Illocutionary act. An illocutionary act is accomplished via utterance with a communicative intention. A speaker may perform illocutionary act to make a promise, offer, explanation, etc, which is as proposed by Austin as illocutionary force. (see more examples of illocutionary acts)
In indicating illocutionary act Searle develops a device called Illocutionary Force Indicating Device (IFID). It is an expression to show the illocutionary force of an utterance is. For example, in the utterance
[1.5] ‘I promise you this’
The word ‘promise’ in [1.5] is identified as performative verb which is one of the devices to identify illocutionary force. It is obviously indicated that the illocutionary force of the speaker is to promise something to the hearer as the speaker describes it explicitly. Sometimes one doesn’t explicitly mention their intention explicitly. When this happens another IFID can be used to identify the illocutionary force of the speaker. These are word orders, intonations, and stresses.
[1.6 a] You’re going!
[1.6 b] You’re going?
[1.6 c] Are you going?
In these utterances can be indicated that the illocutionary force of [1.6 a] is to tell or make decision, while [1.6 b] is requesting confirmation and [1.6 c] is asking about the hearer’s activity in the near future (emphasizing in word order difference).
While locutionary act is the action of making a meaningful utterance and illocutionary act is performing an intentional utterance, perlocutionary act talks about producing the effect of the meaningful, intentional utterance. While making utterance that intent to make someone to drink coffee is successfully performed, the effect is that someone actually drank the coffee is also known as perlocutionary effect. Another example is when a boy says to a girl “You’re beautiful”, if the girl is attracted to the boy usually the girl will blush and feel happy; but on the contrary, if the girl is not attracted to the speaker, then usually she will only say “Thank you” and don’t feel as happy as in the first case. (more examples of perlocutionary acts).
In conclusion, locutionary act is the production of meaningful utterances and expressions (“go away!”, “come here”, “who are you?”, etc) which leads to illocutionary act, the intention of producing meaningful expression (promise, offering, etc), which causes the performance of perlocutionary act, which is the effect of the locutionary and illocutionary act (behavior, feeling, belief, etc).