The 'Shivling' is sometimes wrongly represented as a generative power of nature. In Sanskrit, the word lingam means 'mark,' that which reaches an inference. It symbolizes the omnipresence of formless Lord Shiva.
It also represents the 'Brahmanda,' the universe that gives us all the strength and determination. As the myth goes, 'Lord Shiva' speaks to his devotees silently and is deeply seated in the souls (Atma) of every human being. It's for us to realize his presence and ask for his grace.
The ancient Puranas describe the 'Shivlingam' as something devoid of odor, color, and taste and stand for nature itself of which we are a part. It is also called the cosmic egg where the male and female power unite for it's creation and which signifies truth, knowledge, and infinity.
The Hindu scriptures have explained the 'Shivlingam' as having three parts that represent three different celestial and spiritual portion. The top portion of the linga is called the 'Brahma Pitha' who is the embodiment of knowledge; the middle portion is called the 'Vishnu Pitha' that represents the actual truth of creation, and the lower portion is called the 'Shiv Pitha' the symbol of infinity.
It is prescribed in the Hindu scriptures to concentrate deeply on Lord Shiva as that gives us enlightenment and mental strength as also salvation. Therefore ancient sages and hermit sat for 'dhyana' or meditation in places where the 'shiv linga' has been installed.
The Hindus worship the shiva lingam every Monday and Friday and also on Shiva Ratri to endow them with his strength(shakti) and determination( as he is thought to be the embodiment of patient and determination). Young girls in India also ask for his blessings on this day and wish for a loving and dedicated life partner. Lord Shiva bestows his blessings through a little devotional prayer to the Shivlingam.