My suggestion is to take a look at StringRequests. Here is an example of how to send things to a PHP file, which updates a database, or can do whatever:
LoginRequest.java:
package com.example.your_app.database_requests;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;
import java.util.HashMap;
import java.util.Map;
public class LoginRequest extends StringRequest {
    private static final String LOGIN_REQUEST_URL = "http://example.com/Login.php";
    private Map<String, String> params;
    public LoginRequest(String username, String password, Response.Listener<String> listener) {
        super(Request.Method.POST, LOGIN_REQUEST_URL, listener, null);
        params = new HashMap<>();
        params.put("username", username);
        params.put("password", password);
    }
    @Override
    public Map<String, String> getParams() {
        return params;
    }
}
To send the StringRequest and get a return value:
Response.Listener<String> listener = new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    try {
                        JSONObject jsonResponse = new JSONObject(response);
                        boolean success = jsonResponse.getBoolean("success");
                        // Anything else that your php file returns will go here (like the boolean success)
                        if (!success) {
                            Log.e(TAG, "Could not login.");
                        } else {
                            Log.e(TAG, "Logged in.");
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            };
            LoginRequest loginRequest = new LoginRequest(username, password, listener);
            RequestQueue requestQueue = Volley.newRequestQueue(context);
            requestQueue.add(loginRequest);
Login.php:
<?php
    $password = $_POST["password"];
    $username = $_POST["username"];
    $con = mysqli_connect("website.com", "dbusername", "dbpassword", "dbtable");
    $response = array();
    $response["success"] = false;
    /* Do something */
    $response["success"] = true;
    echo json_encode($response);
?>