Hajj is one of the best forms of worship and is one of the most sublime deeds because it is one of the pillars of Islam that Allah sent Muhammad (peace be upon him) with. A servant's religion is incomplete without it.
A form of worship is only acceptable when the following is true.
One devotes it to Allah alone, with a desire for the Hereafter. It cannot be done with the intention of being seen among people or for worldly gain.
One follows the Prophet's example, in words and deeds. This cannot accomplished without knowledge of the Sunnah.
The way in which the pilgrimage to Mecca can be performed and the regulations governing its rites vary according to where the pilgrim lives or whether intends to make umrah along with Hajj or whether one wants to offer an animal sacrifice or not. These variations have been traditionally grouped into three categories and referred to as the three types of Hajj, namely Hajj Ifrad, Hajj Qiran and Hajj Tamattu‘. Any one of these three methods, if performed according to their regulations without doing any actions which invalidate them, fulfill the compulsory Islamic requirement of Hajj once in a lifetime.
There are three forms of Hajj: Tamattu', Ifrad, Qiran
A pilgrim wears ihram for umrah only during the months of Hajj, which means when they reach Mecca, they make Tawaf and Sa'i for ‘Umrah. They then shave or clip their hair. On the day of Tarwiyah, which is the eighth of Dhul-Hijjah, they put on the Ihram again, but this time for Hajj only and carry out all of its requirements.
A pilgrim wears ihram for Hajj only. When they reach Mecca, they perform tawaf for their arrival and sa'i for Hajj. They don't shave or clip their hair as they don't disengage from the ihram. Instead, they remain in the ihram till after they stone Jamrat Al-'Aqabah on the Eid day. It is permissible for them to postpone their Sa'i for Hajj until after his Tawaf for Hajj. But a lot of people prefer to perform it earlier for convenience and ease later on.
A pilgrim wears the ihram for both umrah and hajj or wears the ihram first for umrah, then makes intentions for hajj before the tawaf for hajj. The obligations on those performing Qiran are the same as on those performing Ifrad, except that it is compulsory for those performing Qiran to sacrifice an animal while those performing Ifrad are not obligated to do so.
The best of the three forms is Tamattu'. It is the form that the Prophet (peace be upon him) encouraged his followers to perform. Even if a pilgrim makes intentions to perform Qiran or Ifrad they are allowed to change their intentions to Tamattu'; this can be done even after they have performed tawaf and sa'i.
When the Prophet (peace be upon him) performed tawaf and sa'i during the Farewell Hajj with his companions, he ordered all those who hadn't brought sacrificial animals to change their intentions for Hajj to intentions for umrah, cut their hair, and disengage from the ihram till hajj.
He said, "If I hadn't brought the sacrificial animal, I'd have done what I've ordered you to do."