As I said in your other topic, you also want to make sure you are recording at a high enough level in the first place, or you will hear hiss when you amplify.
Make a test recording first. Play a loud part of the tape then use the Audacity Recording Slider (microphone symbol):
to adjust the recording level so that the recording meter reaches a maximum of about - 6 dB.
No. Amplify or Normalize set the loudest peak in each track to the level you specify.
Having the peak in each piece at the same level (for example, -3 dB) does not make every piece sound equally loud, especially with music.
If you want to specify equal loudness in Audacity you either have to add the ReplayGain plugin to Audacity, or export the MP3 files as they are then adjust their volume with MP3Gain.
Gale