The Electronics Involved in Instruction Fetching
If you want to make a connection between software code and electrons, you need to start with basics of digital logic. 

First, there are no "electrons" in digital design, electrons are abstracted to "voltage levels" on some wires, or "nodes" as they are called. More, the "voltage levels" are further reduced/abstracted to only two levels, "HIGH" and "LOW", which are separated by some threshold, so the levels that can be "registered" by "flip-flop" are only HIGH or LOW, representing logical "TRUE" (or "1"), and "FALSE (or "0"). And nothing in between. So all signals in a digital design are assuming "1" or "0" values, on every wire connection. From this point you should forget about "electrons" or "voltage differences".

Then you need to comprehend how the basic digital logic elements work.

There are combinatorial LOGIC elements that take two or more inputs, and output some simple result in accord with their TRUTH TABLE. How do they do it should not concern you at this level, electrons are abstracted out, and a bunch of carefully interconnected transistors do the job. These basic elements are NORs, NANDs, etc. And "decoders"/"encoders".

There are "memory elements" like flip-flops, which can "remember" the state of input logic value after a "clock" event, usually a transition of some logic signal from low to high, or from high to low. The input value is "latched" now. A group of certain number of FFs constitutes a "register". If the clock doesn't toggle, the FF will remember the logic state.

There are elements that can pass a data signal if enabled by some other signal, or block the signal propagation if disabled. These elements are called "mulitpexors" (or "MUXes"), or "bi-directional bus drivers". They are used to direct data flows (wire connections) between different "units" or "registers", to disconnect logic units from data busses and/or connect the bus to another destination or source of data.

Once you master an understanding of functionality of these basic elements, you can start thinking of how data can be stored in arrays of registers, how to address the individual registers (or "memory locations"), and get the stored data on a bus. Then "fetching" an instruction or operand would be to address the memory location by one set of wires, force the memory to output the data it contains, direct/enable the bus of data wires to desired destination (as input to decoder), and latch these data for decoding. This is done by a carefully-designed  sequencer, or "Control Unit" from your previous question. 

When some explanatory text says "sends command", or "memory returns" something, it all means that some digital block enables distinct voltage levels on a bunch of wires, and another block (as memory cell/register) asserts its content on another bus (bunch of wires for data). A lingo "CPU copies" means that these instant data values were latched into a dedicated register (a separate bunch of FFs) in proper moment, and remain there while the data bus can be connected to another memory location or another source/operand. The electrons here are needed only to remember that signals propagate at finite speed, and there needs to be some time for the levels to settle to robust digital levels before latching the data up. 

All this is written in hundreds of books, so I hope you are not mocking people here asking to explain the entire digital electronics in on page. But I tried.