How can i create file extention to my application like (*.mytxt , *.myavi)& how can i made this file defaultly open with my application?

This is the code to register extenstion
=============================================
int RegisterExtenstion( )
{
HKEY hkey;

if (ERROR_SUCCESS==RegOpenKey(HKEY_CLASSES_ROOT,".mfe",&hkey))
{
RegCloseKey(hkey);
AfxMessageBox("This Extension is already registered");
GetDlgItem(IDOK)->ShowWindow(SW_HIDE);
return ;
}
CString sExt=".mfe";
CString sDescription="My File Extension";

sDescription.Replace(" ",""); //revoing spaces in Description
sExt.Replace(" ",""); // sExt – extension to register

sExt.Replace(".","");
sExt="."+sExt;


CString app=GetCommandLine(); // Getting the application Path

app.TrimLeft(_T("\"")); app.TrimRight(_T("\""));

CString str,strIcon;
str.Format(_T("%s"),app);
PathRemoveFileSpec((LPTSTR)(LPCTSTR)str) ; //for this #include "Shlwapi.h" //#pragma comment(lib,"Shlwapi.lib")
strIcon.Format(_T("%s\\Sample.ico \0"),str);//place "Sample icon" in exe folder

app+=" \"%1\"";

RegOpenKeyEx(HKEY_CLASSES_ROOT,"",0,KEY_QUERY_VALUE,&hkey);
DWORD dw;

RegCreateKeyEx(hkey, sExt.operator LPCTSTR() , 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL,&hkey, &dw );

CString key=sDescription;

RegSetValueEx(hkey,"",0,REG_SZ,(BYTE *)key.operator LPCTSTR(),
key.GetLength());
RegCloseKey(hkey);

RegOpenKeyEx(HKEY_CLASSES_ROOT,"",0,KEY_QUERY_VALUE,&hkey);

RegCreateKeyEx (hkey, key, 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL, &hkey, &dw);

RegCreateKeyEx (hkey, "shell", 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL,&hkey, &dw);

RegCreateKeyEx (hkey, "open", 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL,&hkey, &dw);

RegCreateKeyEx (hkey, "command", 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL,&hkey, &dw);

RegSetValueEx(hkey,"",0,REG_SZ, (LPBYTE)(LPCTSTR)app,app.GetLength());
RegCloseKey(hkey);

RegOpenKeyEx(HKEY_CLASSES_ROOT,key,0,KEY_QUERY_VALUE,&hkey);
RegCreateKeyEx (hkey, "DefaultIcon", 0L, NULL,
REG_OPTION_NON_VOLATILE,
KEY_ALL_ACCESS,
NULL,&hkey, &dw);

RegSetValueEx(hkey,"",0,REG_SZ, (LPBYTE)(LPCTSTR)strIcon,strIcon.GetLength());
RegCloseKey(hkey);; return 1; }