Look at the number Mod 1. When you look at a number Mod n, you just divide by n, and look at the remainder. So here you divide by 1, and the remainder is just the fractional part. The best way to do this depends on the language.
Simple paint a long horizontal black stroke on a scratch piece of paper and then once it dries paint your watercolors colors in short vertical strokes on top of it. If the paint appears to sit on top of the black stroke the paint is opaque.
GIF animation of an Apollonian sphere packing with transparent background. Transparency is possible in a number of graphics file formats. The term transparency is used in various ways by different people, but at its simplest there is full transparency i.e. something that is completely invisible. Of course, only part of a graphic should be fully transparent, or there would be nothing to see.