What will be required to create electronic circuits, devices, etc.? What do you need to buy?

Question

Do it yourself

Creation of devices with programming*

Answer 1

You need to buy a library subscription. Or brains.
This is not an insult, but a broadcast answer to a broadcast question. To develop some kind of device, you need to respect everyone and not be stupid.
If you turn the question from a philosophical one into a specific one, it will be possible to advise what specifically to read, buy, do.

Answer 2

Electronic components, on the basis of which you will assemble what you want to end up with. Plus knowledge of electronics and circuitry.

Answer 3

The very first thing that is required is knowledge of technical English - because the documentation for electronic components will have to be read and sometimes it is faster to defame it than to mess around with translators.
For an entry-level "play around", modular devices like raspberryPi or Arduino are best suited. You will also need some modules. It is best to choose popular electronic components for which libraries with sample programs have already been written and they really work. Modifying a library is easier than writing from scratch.
Buy: Arduino Mega2560, Ethernet Sheild W5100, Sim900 Board, Mifare RC-522, Relay Module 8, 128x64 Display ST7920, Key Matrix 4x4, DS1307, DS18B20, USBAsp, Breadboard, wiring,
I have all this for "playing around".
Thus, you can build a project "on the knee" - write a program. If you want to put it into a series, you can always draw the wiring in (some kind of) CAD and order the boards (along with the installation).