What are the endings for the active pluperfect tense?

We have seen how the pluperfect is translated as 'I had x-ed' in the active form.

For all verbs to form the pluperfect you need to have

the perfect stem + the imperfect of the verb 'I am'

The perfect stem is the same for whoever is doing it so for the verb porto, portare, portavi, portatus the perfect stem comes from the verb in the perfect form which is portavi. 

Therefore we will use the perfect stem which is just 'portav' since the 'i' indicates that 'I carried' we do not need this.

Once you have the perfect stem you have to add the imperfect of the verb 'I am'.

So depending on who 'had x-ed' the endings change.

sum, esse, fui are the different forms of the verb 'I am' and the imperfect endings are the following for whoever is doing it.

I was = eram

You (singular) were = eras

He was = erat

We were = eramus

You (plural) were = eratis

They were = erant

Therefore if we want to say 'they had carried' we use

i) the perfect stem: portav-

+

ii) the imperfect of sum, esse, fui for 'they' = erant

So portav + erant = portaverunt (they had carried)