If I have a medication for pain and it says 1-2 tablets every 6 hours, as needed for pain?

That's one way to look at it, but it's very impractical to take one pill every three hours. Especially during your sleeping hours.

I would suggest you follow your actual pain levels, rather than the clock. As an example, pain levels are usually higher first thing in the morning, so I would take 2 pills in the morning. I would also take 2 pills before bed, so you can get the rest you need for your body to heal. This leaves you 4 pills that you can take when you find your pain levels rise during your waking hours, taking either one pill or 2 pills, depending on how intense your pain levels are.

The point is to try to keep a steady, or level amount of pain medicine in your body throughout the entire 24 hour day so you don't end up with high, back and forth fluctuations in your pain levels. Ideally, you should seek a stable level of pain relief that is tolerable, even if not complete

Actually you can do that. You have to keep track tho, because that pill will have different timing then the first pill. You should only have at the most 8 tabs in 24 hrs. However, you'll probably find that if you take 2 at once you will have better pain relief.

No, they want a 6-hour gap between the 1-2. 1 every 3 hours will not give you the same benefit.