How do bitshifts work on the electrical layer?
In computers, arithmetic operations are performed by a specific integrated circuit that is placed inside the microprocessor, and is called "Arithmetic Logic Unit". You can have a look at the Wikipedia article on ALU ( https://en.wikipedia.org/wiki/Arithmetic_logic_unit ). As an example it mentions the 74181 ALU, which is a very simple Arithmetic logic unit, able to perform several types of operations, including the left shift, over 4 bits.

I've attached the logic schema of the 74181 ALU (see below). Inputs are A and B, and result is F. Each number is 4 bits long, so there is A3A2A1A0,  B3B2B1B0, and F3F2F1F0. The desired operation is selected with S3S2S1S0:


F = A (op) B
'op' is the desired operation.
If S = S3S2S1S0 = 1100, then 'op' is left shifting.


This is how left shifting works in the particular case of the 74181:


Look at the upper left group of five AND gates and 2 NOR gates.
First AND gate is not exactly AND, because it has only one entry: /A0. Therefore its output is /A0.
Second and third AND gates have 0 output because S1S0 = 00
Fourth AND gate has output /A0*B0, because S2 = 1
Fifth AND gate has output /A0*/B0, because S3 = 1
First NOR gate has output A0.
Second NOR gate has output A0, because /A0*B0 + /A0*/B0 = /A0.


In conclusion, when you have S3S2S1S0 = 1100, the ALU makes F = A + A, which is the same as left shifting.