What do these screw dimensions mean?

Steve's right, M4 x 10 mean that it's a machine screw that is 4 millimeters in diameter and 10 millimeters long and that pretty much every country except the US is on the metric standard. But I doubt the mount is from Europe, as most consumer electronics are manufactured in Asia, though it really doesn't matter. You should be able to find the proper screws in the specialty drawers in the fastener aisle of a home center or an independent hardware store as they often have a wider selection. An M4 x 10 is a pretty common size and you shouldn't have to search too hard to find them, but make sure to look at all of the ones you select carefully, as people often don't put things back in the bins accurately. The threads on these screws are fine and won't survive much over tightening, by the way, so be firm but gentle when using them.

use a number 10 pan head or larger you will be fine be. I recommend using backing of some type also