Error: Objects are not valid as a React child (found: \[object Promise\]). If you meant to render a collection of children, use an array instead." - next.js13

Question

I am making a project using Next js 13 beta version. I know all the components are server components so when I use useState, I need to write "use client" statement at the top but in this case, I got "Error: Objects are not valid as a React child (found: [object Promise]). If you meant to render a collection of children, use an array instead."
"use client";
import { useRouter } from "next/navigation"
import { useState } from "react"
async function addNewStudent(sInfo, refresh){
await fetch('/api/students', {
method: "POST",
body: JSON.stringify(sInfo)
});
refresh()
}
export default async function Student() {
const router = useRouter()
const [sInfo, setSInfo] = useState({
sName:"",
sSurname:"",
sMobile:"",
sEmail:"",
sAddress:"",
sClass:""
})
const handleChange = (event) => {
setSInfo({ ...sInfo, [event.target.name]: event.target.value });
};
const handleSubmit = async (e) => {
e.preventDefault()
await addNewStudent(sInfo, router.refresh)
}
return (
<form onSubmit={handleSubmit} className="relative bg-white rounded-lg shadow dark:bg-gray-700">
<div className="flex items-start justify-between p-4 border-b rounded-t dark:border-gray-600">
<h3 className="text-xl font-semibold text-gray-900 dark:text-white">
Edit Student
</h3>
<button type="button" className="text-gray-400 bg-transparent hover:bg-gray-200 hover:text-gray-900 rounded-lg text-sm p-1.5 ml-auto inline-flex items-center dark:hover:bg-gray-600 dark:hover:text-white" data-modal-hide="editUserModal">
<svg aria-hidden="true" className="w-5 h-5" fill="currentColor" viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" d="M4.293 4.293a1 1 0 011.414 0L10 8.586l4.293-4.293a1 1 0 111.414 1.414L11.414 10l4.293 4.293a1 1 0 01-1.414 1.414L10 11.414l-4.293 4.293a1 1 0 01-1.414-1.414L8.586 10 4.293 5.707a1 1 0 010-1.414z" clip-rule="evenodd"></path></svg>
</button>
</div>
<div className="p-6 space-y-6">
<div className="grid grid-cols-12 gap-6">
<div className="col-span-12 sm:col-span-4">
<label htmlFor="first-name" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Name</label>
<input type="text" value={sInfo.sName} onChange={handleChange} name="sName" id="first-name" className="shadow-sm bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-600 focus:border-blue-600 block w-full p-2.5 dark:bg-gray-600 dark:border-gray-500 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="student name" />
</div>
<div className="col-span-12 sm:col-span-4">
<label htmlFor="last-name" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Lastname</label>
<input type="text" value={sInfo.sSurname} onChange={handleChange} name="sSurname" id="last-name" className="shadow-sm bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-600 focus:border-blue-600 block w-full p-2.5 dark:bg-gray-600 dark:border-gray-500 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="student lastname" />
</div>
<div className="col-span-12 sm:col-span-4">
<label htmlFor="email" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Email</label>
<input type="email" value={sInfo.sEmail} onChange={handleChange} name="sEmail" id="email" className="shadow-sm bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-600 focus:border-blue-600 block w-full p-2.5 dark:bg-gray-600 dark:border-gray-500 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="email" />
</div>
<div className="col-span-12 sm:col-span-4">
<label htmlFor="phone-number" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Mobile</label>
<input type="number" value={sInfo.sMobile} onChange={handleChange} name="sMobile" id="phone-number" className="shadow-sm bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-600 focus:border-blue-600 block w-full p-2.5 dark:bg-gray-600 dark:border-gray-500 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="mobile" />
</div>
<div className="col-span-12 sm:col-span-4">
<label htmlFor="class" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Class</label>
<select id="class" value={sInfo.sClass} onChange={handleChange} name="sClass" className="bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-500 focus:border-blue-500 block w-full p-2.5 dark:bg-gray-700 dark:border-gray-600 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500">
<option selected>Class</option>
<option value="5">5. Sınıf</option>
<option value="6">6. Sınıf</option>
<option value="7">7. Sınıf</option>
<option value="8">8. Sınıf</option>
<option value="9">9. Sınıf</option>
<option value="10">10. Sınıf</option>
<option value="11">11. Sınıf</option>
<option value="12">12. Sınıf</option>
</select>
</div>
<div className="col-span-12 sm:col-span-4">
<label for="department" className="block mb-2 text-sm font-medium text-gray-900 dark:text-white">Address</label>
<input type="text" value={sInfo.sAddress} onChange={handleChange} name="sAddress" id="department" className="shadow-sm bg-gray-50 border border-gray-300 text-gray-900 text-sm rounded-lg focus:ring-blue-600 focus:border-blue-600 block w-full p-2.5 dark:bg-gray-600 dark:border-gray-500 dark:placeholder-gray-400 dark:text-white dark:focus:ring-blue-500 dark:focus:border-blue-500" placeholder="address" />
</div>
</div>
</div>
<div className="flex items-center p-6 space-x-2 border-t border-gray-200 rounded-b dark:border-gray-600">
<button type="submit" className="text-white bg-blue-700 hover:bg-blue-800 focus:ring-4 focus:outline-none focus:ring-blue-300 font-medium rounded-lg text-sm px-5 py-2.5 text-center dark:bg-blue-600 dark:hover:bg-blue-700 dark:focus:ring-blue-800">Save all</button>
</div>
</form>
)
}
When I delete the statement "use client", I got "You're importing a component that needs useState. It only works in a Client Component but none of its parents are marked with "use client", so they're Server Components by default."