One major difference between spoken and written English is that we do not always speak in complete sentences. For example, in a conversation you might mix complete sentences with fragments, groups of words that are not complete sentences.
In this example, you'll see fragments used.
Grocery Cashier: How are you?
Customer: Just fine. ( Fragment )
Grocery Cashier : Will this be cash or charge?
Customer: Cash : Cash. ( Fragment )
Grocery Cashier : Do you have any coupons?
Customer: I don't have any today. What do I owe you?
Grocery Cashier: $83.21. ( Fragment )