How can I Access a Freebsd Server With ssh?

By default, remote root access is disabled for security reasons. However, you can still enable it by configuring sshd.
Enable Root Login

vi /etc/ssh/sshd_config

1	vi /etc/ssh/sshd_config

Replace the in:

#PermitRootLogin no

1	#PermitRootLogin no

with

PermitRootLogin yes

1	PermitRootLogin yes

save and close it.
Auto Start SSH

vi /etc/rc.conf

1	vi /etc/rc.conf

If there is no such a line

sshd_enable="YES"

1	sshd_enable="YES"

add it, then save it.
Restart sshd

/etc/rc.d/sshd restart

1	/etc/rc.d/sshd restart