Can't seem to get any infill to print?

I've tried numerous different prints/settings and I cannot seem to get any infill to print other than the first few layers. I thought I had worked it out when I looked at the preview of one of my prints in Slic3r (Image 1). It seemed to be adding the infill to the hollow sections within the walls. I tried adding more perimeters to fill in this gap to try and trick the software into infilling the main void of the part to no avail. I then created a simple cube (assuming it was a faulty STL file with these voids within the walls) and tried printing with infill. However again, no infill was printed. I've added my infill settings to the image list too as that might help highlight where i'm going wrong!

Any ideas will be greatly appreciated as I'm stumped. I've only been printing a week so apologies if I've missed something simple!

Thanks!

Just though't i'd note, the slicing programme i'm using is Slic3r with a Creality CR-10 printer!

Looks like the model (.STL) is hollow.
Its printing the external surface (perimeters), internal surface (perimeters) and then the infill is the Red filament.
Bottom and top layers will be solid for the number of layers you set in slic3r.
If you want the big void in the midle then you need a model (.STL) that is solid. That will print with only external perimeters and infill.

Note:- Im using internal and external as it would be in the model not as in slic3r settings which uses the term to describe the multiple perimeters. E.G. In a slicer with a seting of 3 perimeters it will refer to the outside perimeter as external and all others as just perimeters.

Thank you for your response! That's down to an improper assumption by myself then, I said I was new to it haha! The assumption was that all 3D Prints should not be hollow i.e. should contain some sort of infill, but obviously that is not the case. Just added a solid block into Slic3r and boom, theres the infill.

Thanks for your help, really appreciated!