Sikhism is a monotheistic religion from South Asia, with its roots fairly new, from the 15th century. The sacred scripture of Sikhism is the Guru Granth Sahib, which is a collection of 6000 line compositions poetically rendered to an ancient North Indian classical form of music.
Sikhism puts importance on faith and meditation on the name of the One Creator. It also stresses the unity of humankind, selfless service, social justice for all, honest conduct and honest livelihood while in a householder's life.  It pays great importance on doing good actions rather than merely carrying out rituals.
Sikhism bases itself on the spiritual teachings of ten human gurus, the first being Guru Nanak. It is believed that the spiritual text of the Guru Granth Sahib, became the literal embodiment of the eternal Guru after the death of the 10th, last human Guru.
There are over 20 million Sikhs in the world, making it the 5th largest religion in the world. Most Sikhs live in the Punjab province of India.
In Sikhism, "simran" is the act of meditating on the words of the Guru Granth Sahib, and it can be expressed musically through kirtan or internally through Nam Japo, as a way to feel God's presence and assert control over the "Five Thieves". The Five Thieves are lust, rage, greed, attachment, and conceit.
Sikhs do not believe that any single religion has a monopoly on Absolute Truth. 
Sikhs believe in reincarnation and karma, similarly to Hinduism and Buddhism, but more stress is put on attaining salvation through grace in human life, a spiritual union with the infinite.
There is much more to Sikhism than is explained here, and it's sure to fascinate you. We've curated some of the best links, videos and books, below. Feel free to visit them and learn more about this fascinating spiritual path.