I have a project for a homemade steering wheel to play simulators. I want to use an incremental encoder to be used on the X axis (direction in the game). To use this encoder, I need a program that automatically loads code on the Arduino to convert it into a USB game controller. For this program, I need BOOTLOADER to be activated. I tried to activate it using my other board, an Arduino MEGA. But I broke down when I found out that MEGA has different connections than UNO, I tried to connect them in series and activate the boot loader in the conventional way, but I was confused by the connections of the two cards. I wonder if it is possible to activate the boot loader in another way? Otherwise, can I activate the boot loader using a MEGA? What connections should I make between UNO and MEGA?
Remembering that I want the boot loader to be activated on the UNO card.
Please use a simplified language, I am a layman in the programming business, on the other forum it seemed that they spoke Greek to me 
Do you have at least one working board now?
Then I would follow Nick Gammon's bootloader install method.
so ... I managed to make the connections that are here: https://www.arduino.cc/en/Tutorial/ArduinoISP
when i clicked load bootloader, it gave a failure message, but written in the code status: Bootloader recording completed.
The video I saw showed that the card appeared in the "device manager" of windows, like Arduino Leonardo Bootloader (COM22) {port used in the video}, after 8 seconds the manager page reloads and appears as arduino leonardo (COM21 ), only. In this video a LEONARDO arduino was used. But for my project I would use a Uno, since they are basically the same. In my case in device Manager, it appears only as Arduino Uno (COM4) {port used on my PC}
And you loaded the Examples > 11. ArduinoISP > ArduinoISP sketch onto the Arduino that will be acting as the ISP?
See section "Load the sketch" on that web page.
Unless you are using some specialist flasher, Windows device manager will just show whatever it normally does for the UNO or MEGA. Mine just says "USB Serial Port (COM2)" for example.
Which video? Post a link so we can understand what they were doing. Otherwise it's very difficult to answer questions on it.
(running the boot loader)
(programming and configuration)
yes, i loaded this file on arduino.