How can i set up a Solar Panel to charge a 12v DC car battery and power a Raspberry Pi?
Since you have an old car battery, the cost of damaging it by overcharging isn't much ($40?) and that would only happen if it got a lot of sun over weeks.  A small home solar system might have thousands of dollars of batteries, so standard practice has long been for those to always have charge controllers.

For small systems the cost of a charge controller used to be significant so it was common to forego it in favor of simplicity.  However, there are now very - inexpensive -   controllers which no longer as easily justify the old practice.

If you can afford an additional $25, you might as well do it right.  Also, it would come with instructions on what to do.