Please help me to understand this MFC code

void CMFCSample1Dlg::OnBnClickedWrite()
{
	UpdateData(TRUE);

	if (m_vckWriteFile) {
		CString name;
		m_cbWriteFile.GetWindowText(name);
		CFile file;
		if (file.Open(name, CFile::modeRead) == FALSE) {
			return;
		}
		TCHAR Buff[4096];
		DWORD dwLen;
		dwLen = (DWORD)file.GetLength();
		if (4096 < dwLen) {
			file.Close();
			return;
		}
		file.Read(Buff, dwLen);
		file.Close();

		DWORD r = PrtWrite(Buff, dwLen);

		TCHAR buf[64];
		GetErrorMessage(r, buf, 64);
		CString mes;
		mes.Format("PrtWrite(<%s>, %d): %d\n<%s>", name, dwLen, r, buf);
		MessageBox(mes);
	} else {
		TCHAR Buff[256];
		DWORD dwLen = m_vedWrite.GetLength();
		if (254 < dwLen) {
			return;
		}
		_tcscpy(Buff, m_vedWrite);
		Buff[dwLen] = 0x0D;
		dwLen++;
		Buff[dwLen] = 0;

		DWORD r = PrtWrite(Buff, dwLen);

		TCHAR buf[64];
		GetErrorMessage(r, buf, 64);
		CString mes;
		mes.Format("PBWrite(%s, %d): %d\n<%s>", m_vedWrite, dwLen, r, buf);
		MessageBox(mes);
	}
}