Here is the second of the two most basic general electronics formulas, power:

Power = Voltage * Current

Power is in watts (W).
Voltage is in volts (V).
Current is in amps (A).

Is power a measure of how loud your speaker is? No! It isn't!

It's essentially a measure of how much heat the speaker can handle before it gets so hot that it destroys itself. That is what power is in electronics.

The power rating of a speaker, or a resistor, or any other electronic component, is the maximum amount of power it can safely handle, before it gets so hot it fries itself, potentially melting, smoking, and definitely getting hot enough to burn your skin if you touch it.

The power rating of the resistors in your kit are all 1/4 watt.

We obviously don't want to test this out with a speaker and potentially break a speaker, so in this video below we'll connect some different 1/4 watt resistors to our battery and see what happens.

A little sidenote on the video above - if you connected the 100 ohm resistor for just a few seconds, just until it got hot and you had to let go of it, you didn't damage it and can still use it. But if you were to leave it connected for a few minutes (which... please don't), it's probably cooked and after it cools down you should probably throw it out.

Anyway, now let's actually go through the math, and confirm it correlates with what our fingers felt when we did the heat test.

So again... less resistance means more current, which means more power, which means more heat. We're testing 1/4 watt resistors, which will overheat, damaging themselves and possibly your fingers, if they use .25 watts or more.

With that in mind, let's do one final power calculation - probably the only one that really matters right now. Let's determine the smallest possible resistance we could safely plug into our battery, and thus the smallest actual resistor that we could plug in.

Again, the power rating for the resistor is what's safe for the resistor, not what's safe for you and your skin! A 1/4 watt resistor using slightly less than 1/4 watt of power will probably still be dangerously hot (for you, if not for the resistor itself).