How to insert data using AJAX to phpMyAdmin

Question

<script>
    $(document).ready(function(){
        $("#register-submit-btn").click(function(){
            var mailformat = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/;
            var fname = document.getElementById("first_name").value;
            var lname = document.getElementById("last_name").value;
            var phn = document.getElementById("phone").value;
            var emailid  = document.getElementById("email").value;
            var pass  = document.getElementById("password").value;
            var phoneno = /^\d{10}$/;
            if(fname == ""){
                document.getElementById("first_name_err").innerHTML= "First name not be enmpty";
                document.getElementById("first_name_err").style.display = "block";
                $('#first_name').focus();
            }
            else{
                document.getElementById("first_name_err").innerHTML= "";
                document.getElementById("first_name_err").style.display = "none";
            }
            if (lname==""){
                document.getElementById("last_name_err").innerHTML= "Last name not be enmpty";
                document.getElementById("last_name_err").style.display = "block";
                $('#last_name').focus();
            }
            else{
                document.getElementById("last_name_err").innerHTML= "";
                document.getElementById("last_name_err").style.display = "none";
            }
            if (phn=="") {
                document.getElementById("phone_err").innerHTML= "Phone Number not be enmpty";
                document.getElementById("phone_err").style.display = "block";
                $('#phone').focus();
            }
            else if(phn.length != 10){
                document.getElementById("phone_err").innerHTML= "Phone Number should be  10-digits";
                document.getElementById("phone_err").style.display = "block";
                $('#phone').focus();
            }
            else{
                document.getElementById("phone_err").innerHTML= "";
                document.getElementById("phone_err").style.display = "none";
            }
            if(emailid == ""){
                document.getElementById("email_err").innerHTML= "Email not be enmpty";
                document.getElementById("email_err").style.display = "block";
                $('#email').focus();
            }
            else if (!mailformat.test(emailid)){
                document.getElementById("email_err").innerHTML= "Invalid Email";
                document.getElementById("email_err").style.display = "block";
                $('#email').focus();
            }
            else{
                document.getElementById("email_err").innerHTML= "";
                document.getElementById("email_err").style.display = "none";
            }
            if(pass==""){
                document.getElementById("password_err").innerHTML= "Password not be enmpty";
                document.getElementById("password_err").style.display = "block";
                $('#password').focus();
            }
            else{
                document.getElementById("password_err").innerHTML= "";
                document.getElementById("password_err").style.display = "none";
            }
            $.ajax({
                type: 'POST',
                url: 'userinfo.php',
                data: 'firstname=' + fname+ 'lastname=' + lname+ 'phone=' + phn+ 'emailid=' +emailid+ 'password=' + pass,
                success: function(data){
                    alert(data);
                }
            }); 
        });
    });
</script>

How can I save in my admin using AJAX? I'm new for this language when click on submit button getting error not data are not stored in database.

I have created sign up form and user enter values the validation is perfectly working now I need to send the data to database.