I'm not sure I want to delve into the matter of past vs perfect at the start of this (see the bottom of this answer for this detail).
Let's consider the phrase that you have:
We can make a whole sentence for what's being said,
We can translate this into English as
The character 右 is a ...
According to Kunihiro there are 9 usages for ーた form.
A situation completed in the past or that lasted for a certain length of time in the past:
Haha ni tegami o kai-TA ‘I WROTE a letter to my mother.’
Habitual repetition in the past:
Ano koro wa yoku undoo si-TA ‘I USED TO EXERCISE frequently in those
A situation that occurred under a certain ...