Sorry for how crude the graph is: it's not accurate at all because I did it on plain paper! It looks like they want a line graph. A log graph is basically following a logarithmic scale, i.e. instead of numbering it:
Linear (normal): 2000, 4000, 6000, 8000, 10,000, 12,000, 14,000 etc
it can be numbered
Logarithmic: 2000, 4000, 6000, 8000, 10,000, 20,000, 40,000, 60,000, 80,000, 100,000.
In other words, log scales let you skip up from small numbers to high numbers to give a more linear graph. Also notice that I've put a little squiggle on the y axis. This indicates that I've missed 0 - 1000 because there are no values below 1000 in the table
Also note that the y axis reads "log(number of tests)".
That's my graph. Hope this helps and I'll reply quicker now if you have any other questions!