Before we say what attention is, we might want to say first just what attention is not.
Attention is not something that does our actions since we can perform actions that require no attention such as repetitive actions of a mechanical nature. We can act in one way while our attention may be detached from this action and be directed onto something else.
Thus attention is not a functional action. There is no "function of attention".
Attention is not the same as Being since attention can fluctuate from moment to moment, whereas Being does not fluctuate. Being is what it is, that is, Being is the inherent measure of the potentialities within any given whole. Being may have a range of expression, as determined by it's quality (it's inherent potentiality for qualitative experiences), but Being does not fluctuate as attention does.
Thus attention is not a state of Being.
Attention does not necessarily depend upon consciousness. For example, we may be conscious of where our attention is directed or we may not. We may be attentive to a particular task that we are performing but, yet, we may be unconscious of ourselves performing it. Or we may be both attentive to our task and also conscious of ourselves being attentive to it while we perform it. Thus we may be either consciously attentive to an action that we are performing or we may be unconsciously attentive to it.
Consciousness may shift from one state to another with a certain release of energy, since consciousness is a form of energy. But one may not necessarily be attentive to this shift when it is occurring. One may be attentive to the shift while the shift is happening or one may not be. It often happens that we become attentive only AFTER a shift in consciousness occurs.
Thus attention does not necessarily depend on consciousness.
Attention has a certain direction. Attention is voluntary and volitional. However, consciousness is neither voluntary or volitional, nor does it have either direction or place. Consciousness is simply what it is. Consciousness is a certain quality of existence, analogous to the different qualities of energy in the frequency spectrum.
There are as many different states of consciousness as there are levels of energy. Consciousness is a form of energy and as already stated, attention is not dependent on consciousness.
Thus attention is not an energy nor is it an activity. There is no such thing as the "energy of attention".
Attention may be viewed as the simplest and perhaps the most primitive POWER of the Will. As such, attention is neither an activity nor is it an energy, but it is a power that establishes a RELATIONSHIP between the two.
Attention, like the focusing of a lens that directs light, is a power of the Will that can direct energy and activity but it is different from either.