I made a song with a beat I found off YouTube, I converted the video to mp3 and recorded my vocals over it in audacity, when I play the beat alone, it sounds great, when I play my vocals alone, it sounds great, but when I play them together, there is a bunch of random crackling/static. Please help 
The crackling could be clipping : if that is the problem the meters will go into the red …
If that is the problem turn down the gain sliders
on your tracks.
I actually feel as if I have no brain cells at all. Even though this was a very simple fix, you are my savior, thank you sooo much
Right… Mixing is done by summation* so normally you need to reduce the levels in half (-6dB) before mixing. Or, you can export to floating-point WAV (which can go over 0dB without clipping, re-import and Normalize or Amplify to bring-down the peaks, then export to MP3 or whatever format you want.
I converted the video to mp3
As you may know, MP3 is lossy compression. It’s best to work with WAV (or other lossless formats) and if you want MP3, compress ONCE to MP3 as the last step. (YouTube audio/video is compressed so you can’t avoid that, but you can minimize the intermediate compression.)
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- Analog mixers are built-around summing amplifiers, but mixers have separate level controls for each input channel, plus a master level control so technically/mathematically its more like a weighted average than a simple sum.
Yes I am actually stupid right now, I thank the both of you so much