The right key(s) to enter the BIOS system setup depend on who made the motherboard and which company supplied the BIOS Chip.
The most common keys are the delete (Del) key, however many INTEL motherboards use the F2 key to enter BIOS and I've occasionally seen F10 used as well, although on some INTEL motherboards, F10 will take you to a bootable device menu instead of the BIOS Setup.
Use of the F8 key is very rare for BIOS, as all versions of Windows use the F8 key to start Windows in the SAFE Mode.
You'll have to experiment to see which one yours uses, unless you have a manual for the system or the motherboard, in which case you can usually find the answer for your particular system.
Unfortunately, most systems come out of the box with quick boot (sometimes called "quiet boot") and splash screen enabled, which doesn't give you very much time to hit the right key before Windows starts booting up. If you see the "Starting Windows" screen, you've already missed the BIOS setup key opportunity and you'll have to restart and try again.
Lastly, if you're not familiar with all the options contained in the BIOS setup once you get there, be very careful, as selecting the wrong values can render your system unstable, or worse, unbootable. If this happens to you, you can almost always get back into the BIOS, even if Windows won't boot or crashes. Most BIOS setup programs have an option to load what is called "Setup Defaults" which are the most stable settings for your motherboard. Start from there, make a note of what each setting is on a piece of paper and only change one thing at a time. After you've observed the results and are satisfied that the machine is working okay and not crashing or unstable, then you can go back into the BIOS and make another change.
Some BIOS manufacturers also include an option called "Optimum Defaults". If your setup includes both "Setup Defaults" and "Optimum Defaults", the "Optimum Defaults" settings will give you the most performance while retaining system stability.
If, on the other hand, your system ONLY includes an option for "Optimum Defaults", then this is realy the same as the "Setup Defaults" I mentioned earlier. Confusing? Yes, I'm afraid so.