A ref is a way to access a DOM element or a React component directly. Refs allow developers to associate a name or ID with any given component, enabling them to refer back to it later on if needed. This is especially useful when dealing with dynamic or unpredictable user inputs – such as text input fields – where the contents may change at any time, thus requiring quick reactions from the code behind it. 

There are two ways to create refs in React: using the createRef method or using the useRef hook. 
Here is an example of creating a ref using the createRef method: 

import React, { Component } from 'react'; 
class MyComponent extends Component { 
constructor(props) { 
super(props); 
this.myRef = React.createRef(); 
} 
handleClick = () => { 
this.myRef.current.focus(); 
} 
render() { 
return ( 
<div> 
<input type="text" ref={this.myRef} /> 
<button onClick={this.handleClick}>Focus</button> 
</div> 
); 
} 
} 
export default MyComponent; 

In this example, the ref is created in the constructor and it is assigned to the myRef property of the class. The ref is passed to the input element using the ref attribute. The current property of the ref is used to access the underlying DOM element. The handleClick method will trigger the focus method of the input element. 
It's important to note that refs should be used sparingly, and only when necessary. If you can solve a problem using props, state, and component lifecycle methods, it's likely a better solution.