Declaring a class for use in multiple code files

Greetings,

I'm using the following code in a separate file to declare a namespace for writing output files:

using System;
using System.IO;

namespace AutoWriteToFile
{
    public class FileWriter
    {
        // Set this to false to stop writing to file
        private static bool _WriteToFile = true;
        private TextWriter tw;

        void WriteToFile(string FileDest, string StrOutput)
        {

            if (_WriteToFile)
            {                

                try
                {
                    // create a writer and open the file
                    tw = new StreamWriter(FileDest);

                    // write a line of text to the file
                    tw.WriteLine(StrOutput);
                }
                catch (Exception ex)
                {
                    ex.Message.ToString();
                }
                finally
                {
                    // close the stream
                    tw.Close();
                }
            }
        }
    }
}

My problem is related to declaring the class in other files.  For instance, if I want to use this routine in Form1 I would declare the namespace:

using ....
using AutoWriteToFile;

... But how should I declare the class in the Form1 class so I can access the WriteToFile() function?

public partial class Form1 : Form
    {

        public FileWriter FW = new FileWriter();   ????????????????
       
        public Form1()
        {
               
                InitializeComponent();
        }

        ...
        ...
        public void FormCreate(object sender, EventArgs e)
        {
            FW. ???????  This is not working

        ...
        ...

Thank you!