When I try to insert an image into a block it only fills in half the space. How do I get ithe image to fill the entire horizontal space? Please assume (correctly) that you're talking to a complete noob. Thanks.
It might be an issue of the image's alignment being right- or left-aligned. This means that will have a some automatic padding (white space and margins) put around it. This can be resolved by changing the image's alignment to centered. Whether it's in a multi-column setup or a row by itself, having center alignment will allow it to stretch out all the way to the edge of its current placement.