In the English language, when you want to tell someone something that you've heard, especially a quotation, you might need to use reported speech. It's used when someone tells you something, and then you need to tell a third person what the other person said earlier.
This is fairly simple in English, as long as you know your tenses. For example, if John says "I like pizza" to me, I say "John told me (that) he liked pizza". When I tell another person about my conversation with John, I change the tense.
In the example, John used the present simple tense. Let's look at that first.
Present Simple - Past Simple
If somebody says something in the present simple, I report it in the past simple. John says "I like pizza". Therefore, John said (that) he liked pizza. The pronoun has to be changed because I am talking about John, so the I has to change to he in reported speech.
Present Continuous - Past Continuous
If somebody says something using the present continuous tense, you can report it in the past continuous.
John: "I am eating a pizza"
John said (that) he was eating a pizza"
Will/Won't - Would/Wouldn't
When somebody uses the modal will/won't, you should report it using would/wouldn't.
John: "I will eat a pizza."
John said (that) he would eat a pizza.
Can/Can't - Could/Couldn't
When John uses can/can't, I report his speech using could/couldn't.
John: "I can order pizza."
John said (that) he could order pizza.
These aren't all the tenses we use in English, but they are some of the most common ones. We hope this has been helpful!