Not a dumb question at all!
You start with 1mL in the syringe. You drip in the solution until the target color (deep blue) is achieved. Read the level in the syringe and subtract that from 1 (your starting level). This is the value that you compare to the back of the card; find the nearest reading and that gives you your Ca level. For example; the color changes and your syringe reads 0.15mL. Subtracting this from 1, you determine that you used 0.85mL of solution. Checking the chart, there's a "Titrant Used" value for 0.84 and 0.86 with ppm values of 420 and 430 respectively. Given this, your Ca is somewhere around 425ppm.
Note that if you have an especially high level (for example; your doser pump got stuck on and dosed in a bunch of extra calcium water), you can use another syringe and just add the two totals. Eg; 1mL is 500ppm, so if you used a full syringe and then another 0.20mL, you would use the provided conversion rate of 0.01mL = 5ppm (or 1mL = 500ppm) to determine that your Ca level is around 600ppm (500 + .2 * 500).
Additionally - don't try and get the syringe totally full. There should be a small air gap at the top; this is because the tip of the syringe holds some fluid that the measure doesn't account for. Line up the bottom of the plunger with the 1mL line; not the fluid level. When you reach the color change, take the reading from the bottom of the plunger as well. (You could really do anywhere - it's the difference that matters; not the volume of fluid in the syringe remaining - but starting at 1mL reduces confusion and the potential for math errors.)
