according to poetic edda (modern attribution for an unnamed collection of Old Norse anonymous poems), the two ravens are described as perching on Odin's shoulders that Odin gave Huginn and Muninn the ability to speak.
Two ravens sit on his (Odin’s) shoulders and whisper all the news which they see and hear into his ear; they are called Huginn and Muninn. He sends them out in the morning to fly around the whole world, and by breakfast they are back again. Thus, he finds out many new things and this is why he is called ‘raven-god’ (hrafnaguð).
In the Poetic Edda poem Grímnismál, the god Odin (disguised as Grímnir) provides the young Agnarr with information about Odin's companions. He tells the prince about Odin's wolves Geri and Freki, and, in the next stanza of the poem, states that Huginn and Muninn fly daily across the entire world, Midgard. Grímnir says that he worries Huginn may not come back, yet more does he fear for Muninn:
Hugin and Munin
Fly every day
Over all the world;
I worry for Hugin
That he might not return,
But I worry more for Munin
Odin is called the “raven-god” (Hrafnaguð or Hrafnáss), the “raven-tempter” (Hrafnfreistuðr), or “the priest of the raven sacrifice” (Hrafnblóts Goði; this is surely a poetic way of describing fallen warriors as “sacrifices” to the ravens and other carrion birds, with Odin as a decider of who lives and who dies in battle). In the same vein, ravens are called “the greedy hawks of Odin” (átfrekir Óðins haukar), or else his “swan” (Yggs svanr), his “seagull” (Yggjar már), or – showing how far the bird equivalencies could be stretched – his “cuckoo” (Gauts gaukr)
Sometimes kennings use “Hugin” as a substitute for “raven.” Blood is designated as “Hugin’s sea” (Hugins vör) or “Hugin’s drink” (Hugins drekka). The warrior in battle is “the reddener of Hugin’s claws” (fetrjóðr Hugins) or “the reddener of Hugin’s bill” (munnrjóðr Hugins). Battle is “Hugin’s feast” (Hugins jól). The poets occasionally use Munin’s name in the same way, but Hugin’s is far more common.
Furthermore, the sight of ravens immediately following a sacrifice to Odin was taken as a sign that the god had accepted the offering.
Why was there such a longstanding and intense connection between Odin and the raven, of all species? As those kennings suggest, the answer largely has to do with Odin’s roles as a god of war and death. Ravens, as carrion birds, were present when a battle took place, and were some of its prime beneficiaries.
Yet there’s still more to this connection. Ravens aren’t only birds of gore and carnage; they’re also exceptionally intellectual birds, and Odin is an exceptionally intellectual god.