0dBFS is the "digital maximum". Digital-to-analog converters, analog-to-digital converters, "regular" WAV files and CDs, etc. are all limited to 0dB. If you try to go over, you'll get clipping. (Audacity uses floating-point internally, so it essentially has no upper limit and it won't clip but the sound may be clipped when you play or export the file.)
The catch is - Perceived loudness does not correlate well with peak levels. So, it's not unusual to find quiet sounding tracks that are digitally maximized/normalized. Most CDs and MP3s are 0dB normalized, yet some songs sound loud and other songs sound quiet.
Most modern music is highly (dynamically) compressed.
Dynamic compression makes quiet parts louder and/or loud parts quieter. In practice it's mostly used to make everything constantly-loud without boosting/clipping the peaks, although sometimes the levels are driven into clipping.
are there other effects I can use to achieve the desired result?
You can experiment with
Audacity's Compressor effect or the
Limiter effect* to boost the loudness, but of course that changes the character of the sound. And if you have a homemade recording, you are unlikely to get the kind of loudness that the pros get without severely damaging the sound.
What is the point of the amplifier if I can't make any of my tracks louder without clipping,
You can amplify files that are not maximized, or you can use the Amplify effect to reduce the volume (if you want to match the volume of another file, etc.).
...which is basically a kiss of death for the quality of your track.
That's a matter of taste... Many of us are disappointed by what the
Loudness War has done to music. The constant-loudness gets boring and it makes me just want to turn down the volume. I prefer more dynamic contrast, and IMO the dynamics of live music are one of the things that makes live music sound better than recorded music.
I am trying to amplify audio tracks converted from YouTube.
Lossy compression changes the shape of the waveform making some peaks higher and some peaks lower without affecting the "loudness". So, it's not unusual to loose a couple of dB if you edit and re-normalized the boosted peaks down to 0dB.
* Limiters and compressors usually push-down the peaks, and then you have headroom to boost the overall volume.