Explanation of the onSubmit method on React

JavaScript
1

In this class:

export class Usuario extends React.Component{
    constructor(props){
        super(props)
        this.state = {
            usuario: ""
        }
    }
    onChange(e){
        this.setState({
            usuario: e.target.value
        })
    }
    onSubmit(e){
        e.preventDefault()
        this.props.onSubmit(this.state.usuario)
    }

    render(){
        return <div>
                <form onSubmit = {this.onSubmit}>
                    <input type="text" placeholder="Ingresa tu nombre de usuario" onChange={this.onChange} />
                    <input type="submit" />
                </form>
            </div>
    }
}

I understand clearly what this method does:

onChange(e){
        this.setState({
            usuario: e.target.value
        })
    }

Once the input starts changing the this.state.usuario changes to whatever the user is typing on input.

BUt, what about this one:

onSubmit(e){
        e.preventDefault()
        this.props.onSubmit(this.state.usuario)
    }

I get this method will trigger when the user clicks the “submit button”, but apparently this doesn´t change anything on the state.
Apparently the second line of this function is somekind of function but this.props.onSubmit can´t be a function.

I don´t get what really this is doing? What this line means??

 this.props.onSubmit(this.state.usuario)
2

Why do you think this? It’s JavaScript, and functions are first-class, meaning they can be passed around like any other value.

Bear in mind that JSX is just dressing up a function to look like HTML