Who were the titans and what role did they play in the cosmology of ancient greece?

Hesiod claimed, the word Titan means "Strainer", because they strained and performed some presumptuous, fearful deed and the vengeance would come after it. Where the Olympians lived in Olympus, the home of the Titans was Othrys, their stronghold.

The exact number of the Titans varied from author to author, and they often included some of the children of the Titans. So there are at least two generations of Titans can be considered.

For a generation, the Titans shared the world and created mankind, with Cronus as their leader. Although a number of the male Titans were imprisoned in Tartarus, when they chose to fight a war against the younger gods, known as the Olympians.

According to the Orphic myth, Zeus destroyed the Titans with his thunderbolts, because the Titans had murdered and devoured his son Zagreus (Dionysus). From the smouldering ashes, mankind were created.

(just a note it might me useless information)

The Titans were the deities in Greek mythology that preceded the Olympians. They were the children of the primordial deities Uranus (heaven) and Gaea (earth). The Titans included Oceanus, Tethys, Hyperion, Theia, Coeus, Phoebe, Cronus, Rhea, Mnemosyne, Themis, Crius and Iapetus. To help the mortals with there daily tasks

well that depends on how deep the hole is. you'd first go through te crust of the earth, then the upper mantle, then the lower mantle then the outer core, then the inner cor then you'd be stuck in the core to melt.