Activating your light body is about you seeing yourself as light versus seeing yourself as a physical body. In meditation my goal would be to try to experience myself as light only which means trying not to feel as though I was in a body.
Regarding Eye of Horus Attunement
If you have just gotten attuned and are wondering how you activate your light body understand that it does not happen just because you received an attunement. The attunement should make it easier for you to achieve activating your light body. What else are you working on? Why are you wanting to activate your light body? There is a balance you must achieve. Becoming a clear vessel by working on past unresolved issues is work that for most will take years however activating your light body may make it easier for you to do the rest of the work that is discussed in the Eye of Horus Attunement Manual.
How to Activate Your Light Body
In your daily meditation try to sense yourself as a ball of light. Attempt to get to the point in meditation where you no longer feel yourself physically. Do this daily. How long will it take to activate your light body? Everyone is different. We are all at different stages in our development, not just within this lifetime but with our whole time of existence.