How to add prefix as 0 or many zeroes to a number?

ADD PREFIX TO A NUMBER IN EXCEL

1. Type any number say 9999999
2. Right click this cell containing this number
3. Go to Format cells
4. Click on Number Tab
5. Click on General
6. Then Go to Custom
7. Below Type "General" wud be written
8. Type it as 000000000
9. On typing 9 zeroes we will be getting 009999999