How Odin, god of poetry and inspiration, received the Runes

In the Icelandic Havamal ( words of the High One) it is written that:

I know that I hung on the windswept tree,
For nine days and nine nights,
I was pierced with a spear, and given to Odin,
Myself given to myself,
On that tree, which no man knows,
From which roots it arises.
They helped me neither with bread,
Nor with drinking horn.
I took the Runes,
Screaming, I took them,

Then I fell back from that place.