Edit in JSFiddle

$(document).ready( function(){
    
    alert('the jquery is loading');
    
    // to get/set the form fields value we use val() 
        
    var x= $("#mytext").val();
       
    //alert("printing the text box value: "+x);
    
    //alert("now lets see how to set the text box value");
    
    //onclick event for the button and when u click on it will change the css value.
    $("#mychange").click(function(){
        
        $("#mytext").val("sudheer world");
        
    });
    
    
    
    
    
    
    
    
});

<input type="text" value="hello world" id="mytext"><br>
    <input type="button" id="mychange" value="changevalue">
    
        <p id="mypid"> this is my text </p>