It is an illusion. You are floating freely in the space, but massive mass near-by is causing curvature in space-time. In other words: Time goes more slowly in your shoes, because they are closer to the mass. This causes any movement to be circular movement, which is pressing you to the near-by mass, which you experience as "gravity".

Einstein believed gravity isn't really a force in the same sense as the other three fundamental forces, but a property of space-time. That seems to be a problem because it causes some kind of "incompatibilty" with the others. Trying to reconcile those, efforts has been made to create quantum gravity theories, that view space itself as quantized and in this direction you find strings and quantum loop gravity.

Disclaimer: I'm no expert, just parroting what I found in Wikipedia.

Gravity is one of the essential forces in nature. If you want to explain it in simpler terms it is not possible because gravity is the simpler thing. You can use gravity to explain other things, but you cannot use other things to explain gravity.

The dent in the rubber sheet that the earth currently sits on - hence the whole curvature in spacetime thing. As far as I know no one has figured out or found gravitons yet, so it's just a theory.

Which I assume means there should be a few gravity-deniers out there to give themselves a break from global heating denial. :)

That which maketh the apple bonk the skull most uninvitedly.

Curvature in spacetime.

This video by Vsauce really put it in a way that made it stick for me.

https://www.youtube.com/watch?v=Xc4xYacTu-E