That’s a very open question, and I’m going to take the easy way out:
Jakobson’s functions of language
1. The Referential Function
corresponds to the factor of Context and describes a situation, object or mental state. The descriptive statements of the referential function can consist of both definite descriptions and deictic words, e.g. “The autumn leaves have all fallen now.”
2. The Poetic Function
focuses on “the message for its own sake” (the code itself, and how it is used) and is the operative function in poetry as well as slogans.
3. The Emotive (alternatively called “Expressive” or “Affective”) Function
relates to the Addresser (sender) and is best exemplified by interjections and other sound changes that do not alter the denotative meaning of an utterance but do add information about the Addresser’s (speaker’s) internal state, e.g. “Wow, what a view!”
4. The Conative Function
engages the Addressee (receiver) directly and is best illustrated by vocatives and imperatives, e.g. “Tom! Come inside and eat!”
5. The Phatic Function
is language for the sake of interaction and is therefore associated with the Contact/Channel factor. The Phatic Function can be observed in greetings and casual discussions of the weather, particularly with strangers. It also provides the keys to open, maintain, verify or close the communication channel: “Hello?”, “Ok?”, “Hummm”, “Bye”…
6. The Metalingual (alternatively called “Metalinguistic” or “Reflexive”) Function
is the use of language (what Jakobson calls “Code”) to discuss or describe itself.
“Language is used for communication” is what people default to thinking; that’s the referential function (what is in the world), the emotive function (how I feel about the world), and the conative function (how I want to change the world). And the metalingual function, if you’re talking to linguists.
The other two functions, the poetic and phatic, are not primarily about communication. Or at least, not just about communication.