Why they are called as clinging?
These five masses of clinging help to rebirth and bond creatures into infinitive cycles of births. So they are called stick without known or clinging. Birth helps to give pains like as sick, getting old, death, meeting negative people, losing loved people and obstacles to achieve goals. As wholesome way said, these five masses are stressful. Mind is collaborations of energy packet which rapidly start, stay very little time and vanished. Till we get whole enlighten, creatures go from one life into next life via five masses of clinging. After we attained enlightening state, it becomes five masses only and not clinging. Every creatures bond to hell, hungry ghost realm, animal realm & asura realm cause of creatures think these five masses of clinging as oneself or "I" or idea of soul. It means they think there have steady soul which can control oneself. But Lord Buddha teaches us that there have no soul & have only dependent organism (reasons & results) inside rebirth cycle.

Massive Bodies (Rupa)
In Buddhism simply physical body and its organs are called as massive bodies or Rupa. Organs which are related to five senses are called internal masses while subjected objects are called as external masses. As example eye is internal mass while light rays and object are related external mass. So eye-light, ear-sound, tongue-taste, nose-smells, body-feelings from and mind-mental visualization are called as massive bodies. Massive bodies are created & maintained according to foods which creatures are eating. Basic building blocks are quantum state elements of earth, liquids, heat & air.  

Sensing And Identifying (Vadana, Sangna, Sanskara & Vinghagna)
After internal & external masses impact with consciousness (Vignagna), then it percept (sense or feel) and then identify objects. We say above impacts are as connecting (Sparsha). Then thinking about these impacts & identifies via mind using thoughts are called as volitional states (Cetana). These volitional states help to create new formations in mind & astral plane (Karma or Sanskara) while our thinking process. After thinking, normally we are saying as word from mouth or doing actions from body or both together happens. This thinking, saying & acting help to energy collections as store in astral plane as energy packets called Karma. Karma is mental & astral formations. They are energy packets, they are recorded in multi-dimensional space and time as akashic records. So one being has immense akashic records.
Sensing is mainly three types - positive sensing, negative sensing & neutral sensing. But with six senses, it can be categorized as 18 types. As example eye sensing can be positive, negative & neutral. Identifying is six types - identification from eye, ear, nose, tongue, body & mind. Collecting karma also stores in part of mind related to astral plane like as energy image, energy smell, energy taste, etc. People, who are developed their mind, can read these past karma formations or akashic records. Six sensing, six identifying, collecting as karma are resulted from impact. This process is widely described in dependent organism.
Lord Buddha categorizes five masses of clinging as internal-external, heavy-soft, near-long, canny-uncanny & vanished in past-unorganized in future-originated in present. As example, if you lived in your past life as energy body god then it was external, soft, long, canny & vanished in past. But your current human body is internal, heavy, near, uncanny & originated present. Buddha said all these characterize in five masses of clinging are unsteady, stressful & not-self.
  
  Example... eye + light + consciousness inside eye - perception from eye - identifying sensed object 
  - thinking related to object - formation related karma as energy image.
   
  Real life... eye + car + eye consciousness - sensing from eye - identifying car - thinking about car then create
  likeness related to car via mind as "I also need such a car".
  So negative karma stores in mind and space as lust about car.
  
  Real life... mind + mental image of temple + mind consciousness - sensing from mind - identifying temple as
  Buddhist temple - thinking about temple then mind become calm cause of temple as "It is peaceful temple".
  So positive karma stores in mind and space as merits.  
  
Collecting Help To Rebirth
Collecting karmic energies give resources to rebirth. Buddha said “Mind is seed, desires are water and rebirth cycle is paddy field for massive bodies of clinging, Stressful pains are crops." Creatures are rebirth because they have karma to finish. Good karma gives luxury life while bad karma gives pains. Enlightened person don't collect karma. Hence they are not rebirth. Creatures bond to rebirth cycle cause of 20 wrong ideas about five masses of clinging as steady & controllable soul. Those are :  

1-4. Creatures bond to wrong idea as - massive bodies are soul, soul created from massive bodies, soul is inside massive bodies  & massive bodies are inside soul. 
5-8. Creatures bond to wrong idea as - sensing is soul, soul created from sensing , soul is inside sensing & sensing is inside soul. 
9-12. Creatures bond to wrong idea as - identifying is soul, soul created from identifying , soul is inside identifying & identifying is inside soul. 
13-16. Creatures bond to wrong idea as - collecting karma is soul, soul created from collecting karma , soul is inside collecting karma & collecting karma is inside soul. 
17-20. Finally creatures bond to wrong idea as - consciousness is soul, soul created from consciousness, soul is inside mind consciousness & consciousness is inside soul. 
  
But we need to think massive bodies are resulted from earth, liquids, heat & air elements. We need to think sensing, identifying, collecting karma are resulted from impacting. And consciousness is result from sensing, identifying, impacting, volitional states, recollecting and massive bodies (mind & matters or Nama-Rupa). 

Unknowingness
We belong to rebirth cycle cause of - karma seeds, bonds from desires and darkness of unknowingness. Also we accept sensed and identified objects as my things. So wrong sensing & wrong identifying means we think all matters are immortal, pleasure & mine. But truth was all masses are destroying and change with time, therefore stressful (sad) and we can't control above changing, means those are not ours (not mine). When we understand these all "five masses of clinging" are not I, mine & my soul (characteristic of anti-soul or not-self) then we are disgusted about five masses of clinging. Then we will not cling to those. So without cling, collecting karma & desires to worlds, will not happen. Without karma seeds & desires, rebirth is not takes place. So then those creatures become enlightened with hearty right ideas. These were main teachings & investigations of Lord Buddha with his omniscient wisdom.