in my case, i am using openvpn server running at IPCOP. You can see the manual from here.
the first, using PKCs file;
1. install openvpn from synaptec package manager
2. download file pkcs file and configuration from your ipcop machine to /etc/openvpn on zip fle. and you will get 2 file, example con1.p12 and con2ipcop.opvn.
3. copy both of file to /etc/openvpn
4. rename file con2ipcop.opvn to con2ipcop.conf
5. open terminal run the below command
$sudo /etc/openvpn/opevpn con2ipcop.conf
6. you have connected to vpn server and press Crtl+c to close connection
the second, using network manager
1. extrak pkcs file to cert and key file with following command;
openssl pkcs12 -nocerts -in con1.p12 -out userkey.pem
openssl pkcs12 -nokeys -clcerts -in con1.p12 -out usercert.pem
openssl pkcs12 -nokeys -cacerts -in con1.p12 -out userca.pem
2. put the file from step 1 to network manager as following picture
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3. ready to go.