Article 136 empowers the Supreme Court to grant special leave to appeal. In other words, under this article, any person aggrieved by decision of any court/tribunal in India can move to Supreme Court against such decision. However, there must be a substantial question of law involved or gross injustice has been meted out to the party.
Merely filing a Special Leave Petition doesn't mean petition has been admitted by the Supreme Court. First, the court examines the petition and then it decides whether it is fit to be admitted or not. Most if the petitions are rejected in this stage only. The Constitution does not lay down any guidelines for excercise of power under Article 136. This the Supreme Court itself through various case laws has laid down certain guidelines/ per conditions that it should consider before proceeding to grant special leave to appeal. Thus by virtue of various decisions of the Supreme court this power can be excersised when there is "substantial question of law involved " (i.e when there is a constitutional or legal issue involved that can be clarified only by the Supreme Court) or there is gross injustice.
It must be noted that special leave to appeal to the Supreme Court can't be claimed as a matter of right, it is the sole privilege of the court whether to grant it or not. Clearly, the court has absolute discretionary power.