Actually it is off topic for this particular mailing list.... Anyway: 1) your command is ok if you use single quotes when directly putting the encrypted string instead of double quotes
$ sudo useradd -c "your user" -m your_user -p 'encrypted password'
2) or you could use what sugggested by Banyan using command substitution ( `...` or the more Posix compliant and readable $(...) mechanism) that works instead with double quotes
Gianluca