There are already quite some tutorials on how to open the game, so make sure to check them out if you can't figure it out yourself (or maybe you should not use a computer if this is an issue).

This one you can approach in many ways:
- Ctrl + Shift + Esc;
- Right click your taskbar and then Task Manager (image below);
- Windows key and then write Task Manager?;

This one also can be approached in a few ways, but generally - once you open the task manager, you will be in the "Processes" tab. From there, just left click on the "Far Cry Primal", then right click on it and then click "Go To process" and you will be in the "Details tab" and already have the games .exe selected.

Next step is to set correct cores and this one might be tricky and may ask for some trial and error (in case you have more cores or whatever)! Right click on the FCPrimal.exe and then "Set affinity".

A list of CPU cores/processes available will be shows. If your computer has more than 4 and all of them are activated - this might be why your game is stuttering.

What fixed stuttering for me? I selected CPU 0, CPU 2, CPU 4 and CPU 6. Every other one is UNCHECKED!!!! Then click Ok (obviously).

Why? As I said before, these older games were designed for 4 core cpus and why even numbers - I am too lazy to google.
Select them, click OK and try out the game, should be working :)))
Works on my Intel i5-9300H

My source of info is years of gaming and also there were some posts online (steam forum posts about stuttering in far cry games) but there was one which said the CPU Affinity and 4 cores, however, I do not remember where and what and all. So if the inventor of the fix sees this guide and can cite the prime-source - please do, I will post the link and credits here or remove the guide if you give a ♥♥♥♥.