Example of how to implement local database in your Xamarin.Forms applications - http://julianocustodio.com/litedb

MainPage.xaml.cs

        private void Insert(object sender, System.EventArgs e)
        {

            int idCustomer = Customers.Count() == 0 ? 1 : (int) (Customers.Max(x => x.Id) + 1);
            Customer customer = new Customer
            {
                Id = idCustomer,
                Name = EntryName.Text,
            };

            Customers.Insert(customer);
            
            ListCustomers.ItemsSource = Customers.FindAll();

        }