Who is Lord Shiva?
Lord Shiva is someone sitting somewhere?
What is Shiva?
Is he a form?

For centuries, historians and devotees have idealized the image of Lord Shiva. Ash-stained body, tiger skin, crescent moon, snake around neck, third eye, curvy hair, Ganges river flowing from hair, a trident in one hand, Dumroo in the other, and sometimes consumed in cosmic dance and sometimes sits like a rock. Besides this, there are also 1008 names for Lord Shiva to describe his attributes.
To truly understand Shiva, it is imperative to know that Shiva is not limited to three things: name, form, and time. The most important thing is that Shiva is not a person who sits somewhere or in heaven.
What is the meaning of Lord Shiva?
Shiva is sha + ee + va
Sha means Shareeram or Body
ee means eeshwari or life giving energy
Va means vayu or movement
Thus, Shiva represents the body with life and movement.
Shafa means lifeless body. Shiva has life potential, while Shava has no life.
Which leads us to a deeper understanding that Shiva is life, that Shiva is the potential of life, and that Shiva encompasses them all: spirit or general consciousness. The realization of this Shiva Tattva leads to Ananda or bliss.
What is the nature of Lord Shiva?

Arupa: no form
Rupa clothing: the formless form
Sarupa: With form
Shiva's arupa state is such that it is beyond manifestation. The following six distortions do not apply in this case:
Adhi - Antha: the beginning and end
Sankocha-Vistara: contraction and expansion
Prasarana - Abhisarana: spreading and Converging
The Rupa-Arupa condition is a formless state that manifests itself in a form or form that emerges from the form. This is a state of transition from sukshma (subtle) to sthoola (gross).
The state of Sarupa is the state in which Shiva manifests into multifarious forms. Sa means accompanied or accompanied. Thus, the word saruba means manifested form or state.
How can Lord Shiva be understood?

Anavopaya: disciplining the ego
Anava: meditate
Saktopaya: developing attention in silence
Sambavopaya: Freeing oneSelf from Thought
Therefore, Shiva represents the chain from the subtle to the particle and the subtle, and therefore Shiva's therefore requires subtleness and meditation.
This is emphasized through Shiva's description:
"Shivam Shantham Advaitham Chaturtham
Manyante sa Atma Sa vigneyaha
(That state that transcends the three states of wakefulness, dream and sleep and that permeates them all is what Shiva is and is worth knowing).
Since this state is beyond our understanding or has no perceptible or perceptible shape, it is similar to no shape. It can also be called Arupa and is known as Turiya avastha, or the fourth state. In this state, the body is at rest and the mind is at its highest level of consciousness.
Lord Shiva is the place where everything came from, where everything is preserved and everything dissolves. This is Shiva or Shiva Tattva. There is no way you can get out of Shiva at any time because creation consists of Shiva. Your mind and body, everything is made by Shiva Tattva. That is why Shiva is called "Vishwaroopa", which means that the entire universe is what it seems.
Why Lord Shiva Eternal?

The meaning here, there is no head or feet of Shiva. There is no beginning and no end for Shiva. Finally, they meet in the middle and agree that they cannot find Shiva. This is all about Shivalinga. It is a symbolic representation of Infinite Shiva.
How big is Lord Shiva?
While Shiva is not a person, but if one wants to see the scale of Shiva consciousness, one can say:
Brahmananda vyapta deha
Shiva's body beyond the galaxies. The entire universe is the body. All the stars, the nebulas make hair, thousands of suns together, eyes. Water the stomach. The snake is the mind. The world is full of millions of vibrations interconnected with the mind, planets, and even food. Everything is connected to the network.
Rudrashtakam says:
Namami-Shamishannirvan roopam, vibhum vyapakam brahma-ved swaroopam. Nijam Nirgunam nirvikalpam Niriham Chidakashmakshavasam Bhajeham
Meaning: He is the Lord, He is the strongest, it is all over, spread everywhere. No place not found. It is that space, that consciousness where all knowledge is. He was never born and had no qualities. It is a state of samadhi where there is nothing but the inner sky of consciousness. This is Shiva.
Lord Shiva is the entire creation

Also read-Maha Shivratri (What is the story behind mahashivratri