There are 8 Operators (In FM-X the Oscillator and AEG are combined into one entity). Each has an OUTPUT LEVEL... adjustable by your Faders when set to "Element/Operator"

When you see an algorithm like #81, the configuration of the numbered Operator blocks, 1-8, determine which ones will make sound and which ones will not.
A box on the bottom row of the Algorithm is called a CARRIER (it produces sound)
A box on an upper row is called a MODULATOR (it never produces sound)... it applies influence on the Operator below it.

Basic FM: The CARRIER is equivalent to the violin string being played by the bow. It produces vibrations that are audible. CARRIERS produce sound.
The left hand of the violinist is the MODULATOR; it adds 'vibrato' - you cannot hear the vibrato by itself. If you were to stop bowing the string with the right hand - the violin stops making sound. The vibrato on an unbowed string is inaudible. You can see the violinist moving their hand but no sound emanates from the instrument. Modulation can only be heard when the Carrier it is applied to is also producing output.

Look at the diagram of Algorithm 81.

Operators 2, 5 and 8 are CARRIERS and are capable of making sound
Operators 1, 3, 4, 6, and 7 are MODULATORS and are capable of influencing the timbre of the Operator below it; but they make no audible sound.

Look closely at the right side of the screen, you can see that the OUTPUT LEVEL of Operator 1 is at 99... all others are currently at 0
Operator 1 is a MODULATOR - and therefore inaudible.

To get to the screen above. I recalled the "Init Normal (FM-X)" Performance
Press [CATEGORY SEARCH]
Bank/Favorite = All
Tap "Init" > Select "Init Normal (FM-X)"

Move the cursor down to highlight the PART 1 NAME
Activate the "VIEW" (green) just to the left of the Performance Name

You can see the SLIDERS are down on all Operators except Operator 1.

Experiment: Use the Faders on your left front panel to operate the LEVELs.

__ First LOWER them all to 0,
__ Slowly raise Fader 2. This is a CARRIER. Hear the pure SINE Wave - raise it to 99
__ Slowly bring Fader 1 up. Slowly - you will hear the SINE wave tone morph into more complex wave spectra as you slowly raise the level. More and more harmonics are created the more that Operator 1 (inaudible alone) influences Operator 2.

If you were to lower Operator 2 this will remove all sound. Only the CARRIER is ever heard. the MODULATOR changes the character of the tone of the CARRIER it is associated with...

MODULATOR:CARRIER is the most important relationship in FM synthesis. It is how FM can generate complex wave shapes. A Sine Wave has no harmonics - it is the pure Fundamental tone. You will never ever hear a Modulator (same as you cannot hear vibrato alone) you only hear the Modulators effect on the Carrier. You only hear the left hand's influence on the tone of the violin. It is generating vibrato... FM uses Modulators that apply very fast vibrato. The more you increase the Output Level of the Modulator the richer the TONE is in harmonic content. If you double the speed of the MODULATOR, compared to the CARRIER, you wind up outputting PULSE Waves (only ODD numbered Harmonics). If the tuning of the MODULATOR and the CARRIER are the same pitch, then you will output SAWTOOTH Waves (all Harmonics). Harmonics are the whole integer multiple of the fundamental Pitch. Musical mathematics — the harmonic series.

We have a very basic FM-X tutorial that will take you through the fundamentals of Modulator and Carrier (without the mathematics) - using a simple two Operator Stack (Op2 modulating Op1)
Please see this four Part tutorial on the basics in FM:

Mastering MONTAGE: An FM-X Exploration Part 1

Thank you so much for your quick response, Bad Mister! I understand now.

You guys are so helpful!!!

Gary