Update! Need advice to clean this tub if it’s even possible 😩

So this is my childhood home I’ve lived here 19 or so years. As far as I can remember the tub hasn’t been the whitest. I remember my mom used to use bleach and all kinds of cleaning supplies but nothing seemed to get rid of whatever that is in the tub. Could be just old and worn out on the color. Or maybe it’s soap scum or some kind of build up if anyone knows how or what to use to clean my tub it would be very helpful! It’s so embarrassing to have a dirty looking bathtub but we’ve literally tried everything to clean it 😐. Here’s a photo

Update

What exactly is refinishing and can you do it yourself or you gotta have someone else do it? Also on painting it what kind of paint do you guys think will work best? Thanks for the tips!