Abhisheka is a part of Shiva Puja. Without Abhisheka, worship of Shiva is incomplete. During abhisheka, Rudra, Purushasukta, Chamakam, Mahamrityunjaya Japa, etc., are chanted in a particular rhythm and order. Monday is very important for Lord Shiva and the thirteenth day of the fortnight (Pradosha) is very sacred. On these days, devotees of Shiva worship Him with special Puja, Abhisheka, Archana, and offering Prasad. A devotee should be regular in doing Abhisheka for the Lord. He should get by heart Rudra and Chamakam. Ekadasa Rudra is more powerful and effective. In Northern India, every man or woman takes a pot of water and pours it on the Shiva Lingam. This also causes beneficial results and brings about the fulfillment of one's desire. Abhisheka on Shivaratri day is very effective.
‘Linga' means a symbol, in Sanskrit. It is a symbol which points to an inference. When you see a big flood in a river, you infer that there had been heavy rains the previous day. When you see smoke, you infer that there is fire. This vast world of countless forms represents a Linga of the formless Lord. The Shiva Linga is a symbol of Lord Shiva. Lord Shiva is formless. He has no form of His own and yet all forms are His forms. All forms are pervaded by Lord Shiva. Every form is a Linga of the Lord. There is a mysterious power in the Linga, its shape has been designed to induce concentration of the mind. Just as the mind is focused easily in crystal-gazing, so also the mind attains one-pointedness, when it looks at the Linga. That is the reason why the ancient Rishis and the seers of India have prescribed Linga for being installed in the temples of Lord Shiva. A Shiva Linga consists of three parts, the lowest is known as Brahma-Pitha, the middle one Vishnu-Pitha and the upper one, the Shiva-Pitha.
The light of consciousness manifesting out of the transcendental Lord is the Shivalinga. From Him all the moving and unmoving creations take their origin. He is the cause of everything. In Him, the whole world merges itself finally. The Shiva Purana says: "Pitham Ambamayam Sarvam Sivalingascha Chinmayam." The Pitham or the base on which the Linga is installed is the Divine Mother Prakriti, and the Linga is Chinmaya Purusha, the effulgent light and consciousness of the Lord. Linga signifies that the creation is effected by the union of Prakriti and Purusha. The Linga is like an egg. It represents the Brahmanda the cosmic egg.
The popular belief that the Shiva Lingam represents the male sex organ and the base on which the Linga is installed is the female sex organ, Yoni is not true. The Linga and the Yoni do not represent sex organs or sexual union. They may appear to look as if it is so but it is not so. In Tantric literature the Linga and the Yoni is taken as a symbolical representation of Shiva (static) and Shakti (dynamic) the two eternal aspects of the Lord whose union is the cause of the manifested universe. Linga and Yoni therefore is not a symbol of sexual union but the union of two eternal Divine aspects of the Lord. The union of Linga with Yoni symbolizes the creation of this universe by Lord Siva in conjunction His Shakti or Power.