How do ICs work? DEEP explanation.?

Integrated circuits or monolithic circuits work the same way as a circuit made from discrete components, within reason. There are limited values of resistance, capacitance and inductance available with integration though. Also what is available to the designer depends on the manufacturing process. Additionally, ICs have some advantages that are not available with discrete components. Discrete components just means made up from separate transistors and other parts, not integrated into a circuit on a single chip.

Therefore there are specific limitations and changes to the design so that ICs can be manufactured. for example:

Capacitance is often made using a reverse biased semiconductor junction, which is likely to be much less than 100pF.
Transistors with multiple electrodes are available on chips, but not as discrete components.
Resistors and current sources may use a JFET with a zero bias or a current source based on a reference voltage.
There are common circuit blocks that suit IC design like current mirrors, bandgap voltage references and temperature sensors, differential long tailed pairs etc. These are more common in analogue circuits like op-amps.
Inductors may be synthesised from capacitors, or used coils and such with much lower inductance values than discrete components.
Inductors, capacitors and resistances tend to be avoided or adapted to what is achievable by the process.

Connections and components can be smaller and closer together and better matched for gain or temperature, so these can result in improved performance not achievable by discrete designs.

The simulators known as spice simulators were originally intended to allow testing and development of an IC design with simulated components that represent the realistic values in the IC, instead of the different values obtained with discrete components. They simulate any electrical circuit more or less.

Having said all this, it is possible to make logic gates using discrete components and then use the design to make similar circuits as ICs to some degree, especially with the CMOS family. During the very early days this might have been an approach used. You have to work out whether the fets used are enhancement or depletion mode types, as well as N or P channel, and what transconductance and supply voltages will suit to operate as logic gates.

The first link has some examples and test questions.
The second link shows an inverter (NOT gate), a NAND gate and a NOR gate which can be examples for any more complex device.
The third link has a bit about building CMOS gates from discrete components.
Search for other examples of CMOS internal circuits, using an image search.

I recommend you obtain a simulator like LTspice (free, search for it) which will allow you to simulate these circuits on the PC. They allow you to draw the schematic, add power supplies and probes for voltage and current at different points, provide pulse or voltage generators as inputs, and then run the simulation to provide outputs. Parameters and models can be added or changed to make the simulation as realistic as required. Then move on to using actual discrete components on a breadboard if that is what you want. If you look up the data sheets for common devices there are often circuits of the internals, but these are not always able to be made using discrete components - hence the simulator. At first the simulator will seem difficult, but search for tutorials, and try some examples ready made to gain experience. It is a good way to gain insight and learn.

In the real world ICs are so cheap and readily available that no one tries to make them, rather read the specifications (search for data sheets on PDF files) and understand what they actually do. You can be sure they work as specified.

There are also logic simulators, which allow the combinations of different logic gates to be tested. The fourth link explains more, and has a link to a free logic simulator which I have not tried. Note that logic design, like software, is prone to bugs and only experience helps avoid these things. There is no way to determine when the design is "finished". It is a judgement call. A few tips are:
Understand and avoid timing races and event showers.
Understand settling times, propagation delays.
Connect all inputs, used or not, to something at a proper logic level.
Avoid using mechanical switches that have not been properly debounced.
Use power supply bypass capacitors and circuit layouts to avoid interference.
Understand the specifications, especially logic noise margins, power supply noise etc.
Use properly conditioned fast rise/fall pulses only.