Collection variable get specific item

I have a string stored in a variable looking like this: name, email, username

I'm using the regular expression to split the string and storing the result in a collection variable (lets name it collection).

So from my understanding it should look like this now:

collection[0] = name

collection[1] = email

collection[2] = username

So I only want to use the second variable (email) in that collection and put it into an email field for example how do I do that?

From my understanding there must be something like this: ID1 collection but I dont know how to extract that.

Isn't the collection an array of variables?

I read the whole guide of "how to use a collection" but this didnt answer my question.