You asked
Is the nikon d750 good for beginners?
The D750 can be a good first camera if you buy it used. It's an older DSLR, announced in 2014, but its 24.3-megapixel full frame sensor still gives you a lot of image for the money. I'd call it a classic used buy rather than a new starter.
Weigh two things before you commit. The body has no stabilisation, so for slow shutter speeds you'll want a stabilised lens. It's also a full frame DSLR, so it's bigger and heavier than a beginner mirrorless body. Hold one in a shop if you can.
Good everyday lenses for it include the Nikon AF-S 50mm f/1.8G for portraits and low light, and the Nikon AF-S 24-120mm f/4G ED VR as a stabilised all-rounder.
If you want something smaller and simpler, look at the Olympus PEN E-PL9. For buying second-hand, see buying used, and for the wider decision, your first camera.
Written by Claude from this site's pages.