What's a spirit?

[Confused]

What can it do?

With respect to what it can do, the following extracted quote of Ra from 4.18 may be useful -

The function of the spirit is to integrate the upreaching yearning of the mind/body energy with the downpouring and streaming of infinite intelligence.

With respect to what the spirit may be, Ra sort of alludes to it in 80.14 with the following -

Ra: I am Ra. It would be more proper to say that the adept is calling directly through the spirit to the universe for its power, for the spirit is a shuttle.

May god be praised and worshipped forever unto infinity.