Issues sqflite in flutter - flutter

Question

It's been a while I started flutter. And now I am working on the database part. I started with sqflite since it was the ideal one for offline apps but now I can't understand a thing please can somebody help me with this.
import 'package:flutter/widgets.dart';
import 'note.dart';
import 'package:sqflite/sqflite.dart';
import 'dart:async';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
class DatabaseHelper {
static DatabaseHelper _databaseHelper = DatabaseHelper();
static Database? _database;
String noteTable = 'note_table';
String colID = 'id';
String colTitle = 'title';
String colDescription = 'description';
String colPriority = 'priority';
String colDate = 'date';
DatabaseHelper._createInstance();
factory DatabaseHelper() {
if (_databaseHelper == null) {
var databaseHelper = DatabaseHelper._createInstance();
_databaseHelper = databaseHelper;
}
return _databaseHelper;
}
//custom getter for the database
Future<Database> get database async {
// ignore: prefer_conditional_assignment
if (_database == null) {
_database = await initializeDatabase();
}
return _database!;
}
Future<Database> initializeDatabase() async {
Directory directory = await getApplicationDocumentsDirectory();
String path = directory.path + 'note.db';
var notesDatabase =
await openDatabase(path, version: 1, onCreate: _createDb);
return notesDatabase;
}
void _createDb(Database db, int newVersion) async {
await db.execute(
'CREATE TABLE $noteTable($colID INTEGER PRIMARY KEY AUTOINCREMENT, $colTitle TEXT, $colDescription TEXT, $colPriority INTEGER, $colDate TEXT)');
}
Future<List<Map<String, dynamic>>> getNoteMapList() async {
Database db = await this.database;
var result = await db.query(noteTable, orderBy: '$colPriority ASC');
return result;
}
Future<int> insertData(Note note) async {
Database db = await this.database;
var result = await db.insert(noteTable, note.toMap());
return result;
}
Future<int> updateNote(Note note) async {
Database db = await this.database;
var result = await db
.update(noteTable, note.toMap(), where: '$colID', whereArgs: [note.id]);
return result;
}
Future<int> deleteNote(int id) async {
Database db = await this.database;
var result =
await db.rawDelete('DELETE FROM $noteTable where $colID = $id');
return result;
}
Future<int> getCount() async {
Database db = await this.database;
List<Map<String, dynamic>> x =
await db.rawQuery('SELECT COUNT (*) FROM $noteTable');
int? result = Sqflite.firstIntValue(x);
return result!;
}
Future<List<Note>> getNoteList() async {
var noteMapList = await getNoteMapList();
int count = noteMapList.length;
}
}
This is the whole code. I have watched many videos but can't understand a thing. The problem starts when I the database part starts. And while answering the questions please try to be a little simple.