This are my favorites quotes about Agni in the Sama Vedas that contains a good description of Agni, the fire God.
The powerful Agni, the immortal, the parent of wealth, and who is dear to us as a friend.
0 Agni, our purifier and our creator, liberally bestow on us, in reputable ways, food-increasing wealth, such as may make us honor, such as is desired by many and is attended with the highest fame.
Secure the approbation of your own Agni, the lord of sacrifices, the causer of grief, the invader of the gods, the faithful offered of sacrifice for the two worlds, which existed before the clouds, yet without vitality, and who shines with golden radiance.
Agni traverses, by his own mighty, the two worlds, and when he sends down rain he uses his mighty roaring to extend from the farthest to the rest extremity of heaven ; and, great in might, he grows later still in the (ethereal) abode of waters.
Thou, 0 Agni, like the Sun which is white, and another which is red ; thou manifested in the two forms of day and night, and art landed like the canopy of heaven. 0 possessor of food, you preserve the understanding of all men. 0 nourishing, grant that we may receive prosperity-causing presents this sacrifice.
Agni, hast been solemnly ordained by the gods to be invited to all sacrifices performed in the world inhabited by men.
The purifying (Agni); encircled by his white radiant along with the priests, capes from all sin ; arid like the Sun all pure, and brilliant, he shines out from behind the rainy cloud, thou with the seven priests, encircle all created form.
Agni, the trainer of happiness
To summarize, this is how Agni is described in the Sama Veda.
The Sa’ma Veda, Translation by J. Stevenson, 1906