2002 nissan altima only goes into park, reverse, and 3rd gear, why is that?

Hello, are you saying the shift lever only responds in those positions? Or are you somehow able to monitor gear engagement as you drive? If you are having transmission shifting and engagement problem (not the lever but the performance itself); you could have a mechanical or an electrical concern. Too hard to tell without testing and hands on inspection. Ensure fluid level is clean and full.

Move shift lever to desired position!