Marcingee

So I bought a new 1997 Tahoe and I got an oil change
But now I Ben digging around n found few issues
1 my oil pressure goes to almost zero when I drive the car for a while and stop causing check engine light to come on. And when I drive again it goin up to like 20-40
I also found a nice dent on the oil pan could that hav something to do with this?
Was told it can be the oil pump and not drive because ill mess up the engine
Any advice on that?
#2 I have no hot air in the car just cold. Was told it can be the thermostat or a clogged head core? How do I fix that not sure where the heat core is and the thermostat is somewhere at the bottom of radiator?
#3 and I also just found out the car has no coolant in the radiator or the back up coolant container. ( engine was cold when I checked) and also inside the radiator was no coolant but it looked kind of like dirty rusty brownish inside radiator is that bad ?
4 How do I flush the radiator will that fix the nasty look inside it?

SWHouston

Welcome to the Forum.

1)
Hard to say just why your Oil Pressure is so low, but that's right, if you run the engine with the pressure real low (>20lbs) you take a chance of damaging it, so...
For right now, I'd put some high viscosity Oil in it, like a 40-50 W, and see if that will help get the pressure up "for now". This will probably give you some time to get a better diagnosis on just what's going on. Probably rod/crank bearings or a weak Oil pump.
2)
After you run the engine for a while (like 15 minutes), what temperature does it say it's at on the dash gauge ?
It should be reading about 185 deg, and if it is, it's not your Thermostat. If it's not up to that temperature, then you need to replace the Thermostat.
Now, if it is up to 185 and you don't have heat inside, you can "back-flush" the Heater Core (reverse flow fresh water through it) when you dump the old coolant (brownish stuff) out.
3)
Sometimes, there's a valve on the bottom of the Radiator you can use to dump the coolant out of it, or, you can remove the bottom Radiator Hose (just one end) at the Radiator, and dump the coolant that way.
Anyway, you got to get that old stuff out of there, replace the hose, run it till it warms up good, and circulate fresh water through the system to get the majority of dirty coolant out of it. You may have to do this several times to get it clean. It's possible that running fresh water through the system several times, "may" help get your heat going. No promises there through.

Now, here's where you have some choices...
Can you replace your thermostat if necessary ?
Can you locate the supply/return hoses for your heater and back-flush it ?
Can you flush you cooling system like stated ?

If not, then you definitely need to get it done, by a pro.
Then, you need to replace the Coolant with that which you mix yourself, or, buy a Pre-Mixed Coolant and get that in by the time it starts freezing outside.

Think about all this and get back to me
Good luck !