Rooting a device is a process that depends on the phone and manufacturer. On some devices it is flat out impossible, on other it is trivial (those tend to be increasingly rare). The steps usually go something like this

1. Put your phone in developer mode
2. Unlock the bootloader (that's the part that is manufacturer/phone dependent)
3. Use fastboot to install a replacement bootloader (I used TWRP in the past, now I use Orangefox)
4. Once you have a good bootloader, youll be able to install apps from outside Android. This will enable you to give those specific app root access.
5. Install Magisk or superSu or whatever app that gives you root access once booted back in android.

Keep in mind that you can 100% brick your phone doing this and that it'll most likely void your warranty. Do not root your device following this post alone. I tried to answer an ELI5, not a Teach Me How To Do It Like I'm 5.

More information:

• bootloader : that's like the BIOS of your phone. It's software that is used right before your OS (android) launches
• fastboot : that's a mode you can set your phone in that will enable you to run commands via a computer to which your phone is plugged by usb. You can upload custom code to it this way (such as a replacement bootloader)
• https://orangefox.download/