A 650-1300mm like this is about unusable, especially on a D50.
It is a very "slow" lens (small aperture, f/8), and there is no image stabilization, so:
- your only way to check focus is to eyeball it in the viewfinder (which is going to be quite dark), because you cannot even expect the focus confirmation to work.
- given that your D50 is an early DSLR generation, its sensor isn't very sensitive (ISO 1600 max) so even at high ISO you will be using rather slow speeds (likely under 1/100s) while at 650mm you should be using at least 1/1000s to have some probability of not getting too much motion blur.
So, technically, you need a tripod, and very calm wildlife. And a tripod stable enough for a 650mm (not speaking of the 1300mm end) is going to be more expensive than your camera and lens combined.
And I didn't even comment on the optical quality of that lens, which is likely not so good (though it could be good enough for a D50)
From personal experience, even a more recent DSLR with a stabilized 400m requires some decent skill.
My recommendation is to find a second-hand 300mm lens that can work at f/5.6. And then a $50 ghillie suit can be more effective than a $500 lens.