Can't start OpenVPN server on Linux

I am creating my own OpenVPN server on DigitalOcean using this guideline.

I have problem starting from step 10. I just can't start start this server and get error all the time.

The guide says, that I need to execute 2 commands - sudo systemctl -f enable openvpn-server@server.service and sudo systemctl start openvpn-server@server.service.

After execution of the first one it seems like just nothing happens, but after execution of the second one I get this:

sammy@OpenVPN-Server:/etc/openvpn/server$ sudo systemctl start openvpn-server@server.service
Job for openvpn-server@server.service failed because the control process exited with error code.
See "systemctl status openvpn-server@server.service" and "journalctl -xe" for details.

And here is interesting thing, this is result, that I have got while trying to get all openvpn services. As you can see, there is no such - openvpn-server@server.service - service:

sammy@OpenVPN-Server:/etc/openvpn/server$ sudo systemctl list-unit-files | grep openvpn
openvpn-client@.service                    disabled        enabled
openvpn-server@.service                    indirect        enabled
openvpn.service                            enabled         enabled
openvpn@.service                           disabled        enabled

Also I tried to play with it and start other services, but seems hopeless. What should I do?

Here is some configurations from my server.conf file:

sammy@OpenVPN-Server:/etc/openvpn/server$ ls
ca.crt  server.conf  server.crt  server.key

...
# Also tried with just names, still doesn't work
ca /etc/openvpn/ca.crt
cert /etc/openvpn/easy-rsa/keys/server.crt
key /etc/openvpn/easy-rsa/keys/server.key

Thanks to dummyuser I was able to find the error. Using this command - /usr/sbin/openvpn --status /run/openvpn/server.status 10 --cd /etc/openvpn --config /etc/openvpn/server/server.conf --writepid /run/openvpn/server.pid - I was able to list nice log. There, I had error with this server.conf line:

# EXAMPLE: Suppose the client
# having the certificate common name "Thelonious"
# also has a small subnet behind his connecting
# machine, such as 192.168.40.128/255.255.255.248.
# First, uncomment out these lines:
client-config-dir ccd

This option was uncommented, and I had error, that there is no such folder. So, you can either create it or comment this line.