What are the meaning of keys in OVPN file?

I have ovpn file, which allows me to connect to remote server successfully from desktop OpenVPN GUI. Now I want to copy content of this file to OpenVPN client of pfSense. The problem is that fields are not 1:1 correspondent.

I have the following in OVPN file

<key> BEGIN PRIVATE KEY ...<cert> BEGIN CERTIFICATE ...<ca> BEGIN CERTIFICATE<tls-ath> BEGIN OpenVPN Static Key V1

What are these fields?