What is the difference between using { } and ( ) for return statements in JavaScript

Question

I am learning ReactJS and I wanted to know the difference in using curly braces and parenthesis for return statements.
Here is a block of code

class App extends React.Component {
    constructor() {
        super();
        this.state = {
            count: 0
        };
        this.handleClick = this.handleClick.bind(this)
    }

    handleClick() {
        this.setState(prevState => {
            return {
                count: prevState.count + 1
            }
        })
    }
    render() {
        return (
            <div>
                <h1>{this.state.count}</h1>
                <br />
                <button onClick={this.handleClick}>Change!</button>
            </div>
        );
    }
}

export default App

In the handleClick function, return has curly braces and in the render function, it has parenthesis.
Interchanging them in either case gives me an Error.
So...I just wanted to know if there is any difference and which one is to be used when