So I'm pretty new to barbell squat.

I started doing the whole push through heels and spread the floor with your feet and it feels much better however, i dont know what to think of my upper body through the lift

I stick my butt out and think like im sitting in a chair but if i try to keep my chest up and out my back bends inwards and it doesnt feel good on my back. if i let my chest sink down at the bottom i feel like im horizontal with the ground and feels horrible when start to push back up.

flexing my core seems to help a lot the first couple reps however, i cant seem to keep it tight to keep doing reps.

do i probably just have a weak core? (been trying to do an ab roller and planks daily - squatting slowly feels more comfortable but still confused on mental cues)

If your back is hyperextending, than you arent getting tight enough... You shouldn't compensate a tight core by hyperextending.. Work on the valsalva maneuver, do tempo squats, learn to move in 1 movement..

record yourself too, and post it here.

funny how much mental masturbation goes into squat form.

chest up up up, think that your back needs to move up on the ascend, the rest will follow

Thanks so much for the replies everyone!
I'll upload a video next chance i get!

Valsalva aka abdominal bracing. Learn this ASAP

Watch a proper powerlifting vid on how to do it

create a shelf of your traps and pull the bar down into it. Also you might want to try "packing" your neck , as it along with the first thing i mentioned will help you to stay upright on your way back up. To pack your imagine touching your chin to your traps. Sounds bizarre but it helps tons. your head should still be in a position to maintain a neutral spine. Never look at the floor when you squat.