The "Master" thing

The manual calls it "[Load]".
It talks about it on p.31 and 312 of the Eos Operations Manual.
The faders below are for manual cue timing, which is explained on p.259 and p.323-324

If you are using the Element User Manual Version 2.7.2, see page 244:

"Master
The master playback pair can be set as a Proportional Master, Manual Master or Intensity Master (IMaster).
Its behavior is drawn from this setting.

Proportional faders, when the slider is set to zero prior to the execution of a cue, will withhold
playback of intensity data until the fader is raised. Intensity data will then be played back proportionally
according to the level of the fader. Once the fader reaches full, the cue is considered
complete and the cue is released from the manual fader. If the fader is at any value
other than zero when the cue is executed, intensity values will play back normally. If the slider
is returned toward zero, intensity in the cue will fade to the previous level.]

Intensity Masters will master the intensity level for cues during playback. Therefore, intensity
masters set below 100% will proportionally limit playback of intensity data relative to the level
that the fader is set. All non-intensity parameters are unaffected by the fader. Once the fader
has reached full, control of intensity is retained. If the fader is moved toward zero, intensity
will proportionally fade toward zero (not the previous state as per proportional faders).

For Example:
The playback fader is an intensity master and the slider is set at 50%.
When a cue is played back on this fader, intensity values will raise to 50% of their final
values and then stop. As the intensity master is raised/lowered, intensities will increase/
decrease accordingly. Once the slider has reached full, control of intensity is retained.

In Manual Master mode, cues are triggered manually by faders without using the [Go] button.
With a cue list on a fader set to manual master, a cue will fire in manual time when the fader is
moved from 0% or from Full. Timing is scaled. So, if color has a 5 count delay, and the duration
of the cue is 10, the color transition will not begin until the faders manually reach 50%.
Follow and hang times will be ignored when firing a cue with a manual master fader."

Lots of information on TYPES they can be set to like Master, Proportional, Intensity. My p244 again, as per John's reply does not mention Load, Master or Master Fader pair whatever.

I 'm really looking for something simpler. For example, if I have recorded several cues in the ELE2 they're in a list right? So can I assume then that on starting, the 1st cue gets loaded into the left fader and 2nd into right . Then after a GO cue 2 moves to left and cue 3 loads into right? My need may be much more basic then you're anticipating. I'm happy with the proportional thing of setting the faders to achieve some playback scenarios but still not certain the of the philosophy of how and what cues get loaded into them.
Sorry for being vague - this is obviously so basic to most people but not me (yet)

The "the big [Master] button and the faders below" called the "master playback fader pair", part of the "Master Playback Controls".

There is a short video that shows one thing that can be done with them.

The video is here: www.youtube.com/watch

 

Sorry, I was using the wrong manual above.  I've now switched the manual to the one I think you and John are using (as this one covers the Element 2 more accurately).

I'm referring to the manual that says on the front:

Eos Family
(Eos Ti, Eos, Gio, Gio @5, Ion Xe, Ion Xe 20, and Element 2)
Operations Manual
Version 2.7.2
Part Number: 4250M1210-2.7.2 Rev A
Released: 2018-06

...available here: www.etcconnect.com/.../DownloadAsset.aspx

"I 'm really looking for something simpler. For example, if I have recorded several cues in the ELE2 they're in a list right? So can I assume then that on starting, the 1st cue gets loaded into the left fader and 2nd into right . Then after a GO cue 2 moves to left and cue 3 loads into right?"

No: The master is a split crossfader pair.  The left fader controls the intensity upfade, while the right fader controls all intensity downfade actions. The two buttons beneath the master fader pair are [Go] (a triangle) and [Stop/Back] (a square ). The [Load] button (actually says "Master") is located directly above the fader pair.

 

"p.31 Tells me Where and what it is used for. (Loading cues)"

Master Playback Controls
The master playback fader pair is located to the left of the control keypad. The master is a split crossfader
pair. The two buttons beneath the master fader pair are [Go] and [Stop/Back]. The[Load] button
is located directly above the fader pair and is used to load a specified cue onto the master playback.

p.312 Refers to a "Cue List already loaded". But elsewhere it is Noted you can't load Cue lists in Element 2 master pair.

(No, you misread that, I've editing the following quotes from the manual to try to make them clearer).

Note: Element 2's cue list can only be loaded on the master playback fader pair.

The master is a split crossfader pair.  (this next bit is from the Element 1 Manual: The left fader controls the intensity upfade, while the right fader controls all intensity downfade actions.)

The two buttons beneath the master fader pair are [Go] and [Stop/Back]. The [Load] button (actually labeled as [Master]) and playback display are located just above the faders.

"p.259 Not mentioned"

"p.323-324 No mention. Just one 1/4 page ending Chap 16 and p 324 is blank between chapters"

(not in my manual, the chapter ends on 325, 326 is blank).

Start reading on 323 at: "Using Manual Control" or search "Using Manual Control" if you have a different manual, the information is relevant to your question.

Ah! the video. I looked for something like this but couldn't find it - so thanks. Actually been sitting here just 'playing' before my demo tonight and it's coming into focus (pun quite intentional).

It is difficult to describe but tech manuals by nature have to be linear whilst a lot of topics are circular. As teachers we break into the circle by saying "Trust me for now - it'll be easier to explain when I have gone through this". Programmers call it bootstrapping. Bottom line is that no matter how good a manual is unless you can read every single page and remember it you'll need forums likes this!

Ah! the video. I looked for something like this but couldn't find it - so thanks. Actually been sitting here just 'playing' before my demo tonight and it's coming into focus (pun quite intentional).

It is difficult to describe but tech manuals by nature have to be linear whilst a lot of topics are circular. As teachers we break into the circle by saying "Trust me for now - it'll be easier to explain when I have gone through this". Programmers call it bootstrapping. Bottom line is that no matter how good a manual is unless you can read every single page and remember it you'll need forums likes this!