We certainly have the perception that we have freewill.

In the end this is a question that science cannot yet answer and philosophers cannot agree on, so strictly speaking my position must necessarily be one of agnostic.

However, my opinion and personal thinking is that freewill is a matter of perspective and thus an illusion.  I think the entire question arises from a mistaken Dualism and a perceptive misunderstanding regarding the nature of time. 

Dualism. The mind is not separate from the body and thus we are at all times conforming to laws of the universe.  Since we are so entombed in these laws it is impossible for the mind to be free in the sense that freewill means.

Time. The whole notion of freewill rests on the notion of causality. That one thing happens after another and will continue to do so.  As Hume points out in the human sphere we call the expectancy of causality custom, eg that fire will continue to be hot.  However, there is nothing in the Universe to say that this has to be so or that time itself even exists as we perceive it.

So, yes we do have an effect on the world that is determined by our being and actions.

But also we are as much a part of the world and as free as a pebble in a landslide.

Thus while we have an effect we are the result of, and affected by, multiple manifold causes and therefore only a part of the tapestry of the working Universe.