My uncle gave me his old 1980 Schwinn Super Le Tour and i noticed the rear wheel is out of line. Whenever I spin the wheel it rubs against the left part of the frame. How do I fix this problem?

It's likely not seated in the drop outs correctly.
Often, if you are missing the serrated washer on the DS, pedaling will pull the DS forward, resulting in a rub like you have.
Axle nuts may not be tightened down enough either.

Does the wheel rub the same amount for the entire circumference of the rim, or does it only rub in one spot?

If it is the former, the wheel just needs to be centered by loosening one of the axle nuts and centering the rim/tire between the frame tubes (known as the chain stays). Typically, you would loosen the left axle nut, because the right one is butted up against a piece that puts it in a fixed position, while the left can move in a slot (the piece of the frame is called a dropout, and your bike has slotted dropouts). But before you make the adjustment to the left nut, make sure the right one is as far back as possible.

EDIT: If the bike has a quick release, it may need to be adjusted tighter so it will keep the wheel from shifting. You still adjust the wheel alignment by sight using the same technique as a bolt-on wheel.

If it is the latter, the wheel rim is bent. It may be able to be trued, depending on the severity of the deflection.

+1 the key is whether the rim seems to move back and forth as it spins, or whether it runs straight but is off center. The former is a wheel alignment problem, the latter is probably a mounting issue.

However, there's a third possibility if the wheel is straight and properly mounted. It's possible that the wheel is improperly dished, meaning that the rim is not centered on the hub. There's an easy way to confirm. Flip the wheel over right to left and remount it. If it now rubs on the other side of the frame, than the wheel is the problem.

Lastly is the possibility that all is right, except the frame itself is bent to the side.

The most concerning possibility is a tire that is not seated and is starting to expand off the rim. A concern because this can cause a blow out, which can lead to a loss of control. It's rare that an out of true wheel, an out of dish wheel or a wheel miss positioned in the drop outs will cause a catastrophic problem. Andy.