My first circuit...

Almost there. You've got the basic idea. That LED is 2V 20mA, and you're pushing almost 40mA through it. While it may not pop in a dramatic fashion, it's lifespan will probably be reduced. Plus it'll get hot, and when LEDs get hot, they draw more current. That won't be good for it. To find what resistor you need, apply Ohm's Law. R=V/I. R is resistance, in ohms. V is voltage, in volts. I is current in amps. You've got a 9V supply with a 2V LED. So you need to drop 7V at 20mA. So, R = 7/0.02. You'll find standard resistor values near what you need to be 330, 390, and 470 ohms. A good general rule of thumb to do the math, then pick a standard resistor value that is the same or slightly larger the number you calculated.