Enabling SSL / su password

Trying to run a command:
```
ln -s /etc/apache2/mods-available/ssl.load  /etc/apache2/mods-enabled/ssl.load
ln: failed to create symbolic link '/etc/apache2/mods-enabled/ssl.load': Permission denied
```

Tried running
`su -`
but got stuck at the password prompt.

how can I enable ssl?

Thanks!