‘Aisha (radiallaahu `anhaa) said, “The first thing the Prophet (sallallaahu `alayhi wasallam) did on reaching Mecca, was the ablution and then he performed Tawaf of the Ka’ba and that was not ‘Umra (alone), (but Hajj-al-Qiran). ‘Urwa added: Later Abu Bakr (radiallaahu `anhu) and ‘Umar (radiallaahu `anhu) did the same in their Hajj.” And I performed the Hajj with my father Az-Zubair (radiallaahu `anhu), and the first thing he did was Tawaf of the Ka’ba. Later I saw the Muhajirin (Emigrants) and the Ansar doing the same. My mother (Asma’ (radiallaahu `anhaa)) told me that she, her sister (‘Aisha (radiallaahu `anhaa)), Az-Zubair (radiallaahu `anhu) and such and such persons assumed Ihram for ‘Umra, and after they passed their hands over the Black Stone Corner (of the Ka’ba) they finished the Ihram. (i.e. After doing Tawaf of the Ka’ba and Sa’i between Safa-Marwa.
This is Tawaaf al-qudoom (tawaaf of arrival) for Hajj. This is done by the pilgrim who has entered ihraam for Hajj and by the pilgrim who is doing Qiraan, i.e., joining ‘Umrah and Hajj, when he reaches the Ka’bah. It is one of the obligatory duties or Sunnahs of Hajj – there is a difference of scholarly opinion.
More types of tawaaf here.