What is the difference usage and meaning between pişmek and the passive voice of pişirmek?

pişiyor - it is being cooked
pişiriliyor - it is being cooked

 "Pişiyor"       is It is cooking

 "Pişiriliyor"   is it is being cooked  (its passive voice of pişirmek )

But we must clarify the verb pişmek-pişirmek. We call such verbs as Ergative Verbs (Eş işlevsel fiilerl)

Ergative Verbs : an ergative verb is a verb that can be either transitive or intransitive, and whose subject when intransitive corresponds to its direct object when transitive

In Turkish : Transitive (Geçişli), Intransitive (Geçişsiz) Fiiller

               Geçişli fiiller: Nesne alan fiilerdir.. Ne, neyi, kimi sorularına cevap verir (Geçişli verbs takes direct object and can answer the questions of what,to what,to who)

               Geçişsiz fiiller: Nesnesi olmayan veya nesne almayan fiillerdir.. Fiil, neyi, kimi sorularına cevap veremez.. ( Geçişsiz verbs does not take direct object and can not answer the questions of what,to what,to who)

               Lets work on your example ´pişmek,pişirmek´

               I-Makarnayı pişiriyorum. (I am cooking pasta ) 

                     pişirmek = geçişli fiil  ( pişirmek is geçişli (transitive) because it has an direct object which is Makarna(pasta) In here I AM DOING THE ACTION

                   II-Makarna pişiyor. ( Pasta is cooking)

                    pişmek = geçişsiz fiil (pişmek is geçişsiz (intransitive) because it has no direct object. In here PASTA IS DOING THE ACTION.

                  We can classify these type of Verbs into several groups.

                      Bu tür fiilleri, çeşitli gruplara göre koyabiliriz.

Değişim durumunu aklımıza getiren fiiller (The verbs suggesting a change of state)

break, burst form, heal, melt, transform...

Yemek yapma fiilleri (Verbs of cooking)

bake, boil, cook, flambé, fry, grill...

Hareket fiilleri (Verbs of movement)

move, shake, walk...

Araçları kapsayan fiiller (Verbs involving vehicles)

drive, fly, reverse, sail...

Hope this info will help you to understand better.

In English, most verbs can be used intransitively, but ordinarily this does not change the role of the subject; consider, for example, "He ate the soup" (transitive) and "He ate" (intransitive), where the only difference is that the latter does not specify what was eaten. By contrast, with an ergative verb the role of the subject changes; consider "it broke the window" (transitive) and "the window broke" (intransitive).

Ergativity is a little bit difficult concept for those of us who speak nominative–accusative languages like Turkish, English, ...

However in Turkish also we can find some of its examples:

Bu fırsat kaçmaz = This opportunity does not miss

Here the agent ( =you, the one that does the action) is missing from the sentence and the patient ( =this opportunity, object of transitive verb) is the subject of the sentence.

Of course "this opportunity" is not something that can miss itself, here it means:

"you cannot/shouldn´t miss this opportunity"

istemez = it doesn´t want

Here the agent ( =I, the one that does the action) is missing from the sentence and the patient ( =it, object of transitive verb) is the subject of the sentence.

Of course it´s me who doesn´t want it, so here it means:

"I don´t want it"

etc.