what is this port on the head for the one on the right with a bend

Goes to heater core I believe.

Heater core huh? so It is okay to plug? no heater in my car.

heater port

yea it's ok to plug.....but to my amiss ,I believed the "expert' at the fastener store when he told me it was a 3/8 pipe fitting when I had told him it was an old fiat and I am sure it was metric. he scoffed at me as I was stupid, so I took his advise and bought what he SAID was what was needed. NOT
it is indeed metric pipe fitting and the nut is to secure it to the head to keep it from becoming loose.
best bet is to find a rubber cap and hose clamp it down.
unless you are looking for ascetics here.
mikemo

I usually run a rubber line from it back under the back of the rear trunk area and plug it back into the Thermostat so that it keeps flowing water. You can use the wire holders to hold the hose in place wont even notice it.