You learning what they do and so on?

Kind of. Your therapy professional uses the term "parts" because they are parts of you right.

SKR sometimes used the "parts" terminology with me too. here is what she told me

"Since they are a part of you what they do and say and so on is also already part of you. Its what you were already able to do until those parts of you were separated and fogotten. Once you remember what is in those "parts" you will automatically be able to do those things and so on again."

Another professional in the field of DID explained it to me like this -

Kind of like a ceramic apple. The apple starts out whole then the apple gets thrown and it breaks into separated parts scattered and forgotten.

Even though the ceramic apple is now separate and forgotten its still parts of a ceramic apple.

if you find a piece on the floor its still a part of the apple just like the piece of ceramic under the stove, fridge and so on

one day the parts are found and put back together (remembered) to once again be a whole apple.

All the pieces of the apple are there in the beginning.
All the pieces of the apple are there when it is in parts scattered and unremembered.
All the pieces of the apple are there when the parts are put back together to form a whole apple.

Now in terms of a person with DID -
A person may starts out knowing how to add 2 + 2 = 4
then something happens so that 2 + 2 = 4 gets separated and forgotten .. 4 here under the stove a 2 in the fridge, a 2 on the couch, a + in the dining room and = in the car. (All of the parts are there just scattered and forgotten)

The person finds all the parts and puts them back in order (remembers) 2 + 2 = 4.

The person will now always know that 2 + 2 = 4 was separated and forgotten at one time but now will also always know the parts are now together to form the whole.

Hang in there.