I'm a bit late to the party, BUT...
The issue this person is having is that the default plot type is just a "line" which connects points together. If there is only one point, it has nothing to connect it to. You need to add a marker.
Using any of the following characters after your x,y coordinates will produce these markers on your plot:
will just plot a dot at (1,2). You can combine this with line styles and colors to get a lot of variety in your plots. (my favourite is '.-', which puts dots at all the points and connects them together)
Specifically the section on "LineSpec" if you're short on time. It's worth the read as this provides a very simple way to pretty up your graphs a bit (and explains what the character inputs I listed above represent. This is the most common plotting method you're going to use and the syntax for the "LineSpec" works with a myraid of other plotting types, so it's worthwhile to know what's going on.