Doesn't start in freezing cold, battery?
 

I recently purchased a 1992 Oldsmobile 88.
I live in Minnesota and it can get pretty cold here in the winter time.

I will mention, I didn't start my car for a few days since it's been this cold because I wasn't near my car for that time frame.
Is that true or a myth, you must start your car everyday in cold weather in order for it to be able to start at all?

So far I have tried a couple things: 1)Jump starting with another car and 2)Using a car battery charger. Neither haven't really helped, of course hasn't started either way.
I hope I haven't been doing anything wrong or something else might not be working.

Do I need a new battery or what? Is there a specific thing or process I should try for charging my battery?

Kind of hard to diagnose without a lot more info.

What happens when you turn the key?
Do you get any cranking sound at all/only a clicking sound/dead silence?
What are the answers to the above questions when you try to start the car after
hooking a jumper battery to it?
Do the lights/radio/lighter work?
The obvious question, is there gas in the tank? How much?
Does this car have a carburetor or is it fuel injection?

As you can see, there are a lot of variables here.