To speed up the convergence, it is possible to set the applet to repeat the experiment many times for each mouse click. Note that 10,000 rolls can be done at once -- this may take some time, depending on how fast your machine is. It might be more educational to use a smaller number of simultaneous rolls, so that you can watch the histogram converge to a bell-shaped curve.
If only one die is being rolled, the histogram should look flat. For two dice, the histogram should look like the top of a witch's hat. For three and more dice, the histogram will be more bell-shaped looking.
Note that the distribution of a single die (the "discrete uniform") is symmetric and light tailed, so the convergence of the sum of dice to normality is quite fast. Skewed and/or heavy tailed distributions will converge much more slowly.