understanding coroutines

Say I have this coroutine

 protected IEnumerator DoSomething()
 {
     //do stuff 1
     //do stuff 2
     yield return new WaitForSeconds(0.75f);
 }

now if I want to put some of the code in a seperate function, as far as I understand, I have to do this:

 protected IEnumerator DoSomething()
 {
     //do stuff 1
     yield return StartCoroutine(DoSomething2());
 }
 
 protected IEnumerator DoSomething2()
 {
     //do stuff 2
     yield return new WaitForSeconds(0.75f);
 }
 

But I find that rather weird, as I have to start a new coroutine, while I actually just want to split up the code a bit, not start a new coroutine.

Is this correct? I dunno, I just can't seem to grasp coroutines truly.