is this the right way to fetch data while usine usestate hooks? i use usestate hook but i don’t know if this the right way to fetch data

i just wrote the code and fetch usestate data like that cause I didn’t find some source to how doing it
in the form section I use onChange={event => setFirstName(event.target.value)} I don’t know where is the problem cause the data didn’t show up in the database

function OrderCP(props) {
  const [firstName, setFirstName] = useState('');
  const [lastName, setLastName] = useState('');
  const [email, setEmail] = useState('');
  const [mobileNumber, setMobileNumber] = useState('');
  const [adress, setAddress] = useState('');
  const [city, setCity] = useState('');
  const [size, setSize] = useState('');
  const [quantity, setQuantity] = useState('1');






  function onOrderSubmit ()  {
  fetch('http://localhost:3000/orderCP', {
      method: 'post',
      mode: 'cors',
      headers: {'Content-Type': 'application/json'},
      body: JSON.stringify({
        firstname: setFirstName,
        lastname:setLastName,
        email: setEmail,
        mobilenumber: setMobileNumber,
        adress: setAddress,
        city: setCity,
        size:setSize,
        quantity: setQuantity

      })
    })
      .then(response => response.json())
      .then(user => {
        if (user.id) {
         return (
          this.props.loadUser(user),
         <Link to ='/orderCP/orderCompletedCP' /> )
        }
      })
  }