Sidechaining is automating the volume of one track by the volume of another. The way it is used in EDM is to duck the volume of most instruments to the kick drum (and sometime the snare) so it has more punch. I don't know anything about this being used much outside of EDM.

There are many ways to actually do this. It depends on your DAW and the plugins you're using, but here are the most common ways:

- Compressing one track using a sidechain signal. This takes the general dynamic volume level of one audio track, and uses that to automate the volume of the sidechained track.
- Same as above, but using an inaudible sample instead of another instrument
- Simply automating the sidechained track with automation clips. This is what I prefer, as it gives you the most control over the sidechained sound. You can easily change the envelope.

imo just don't bother panning then. a lot of people who aren't deaf in one ear don't pan at all, in edm it's pretty common.

It's not entirely an issue of manual panning though, this could cause problems with stereo effects, e.g. Chorus, unison, etc.

https://clyp.it/ecjsa2bf

This is the best track I've made. I do know that around 2:25, the sidechain stops, which is unintentional. It has been fixed, but my plugins and samples currently aren't loading properly on my new PC, so I can't re-render it right now.
The track itself is mostly complete, I just don't know how to finish it and release it.
What do you think of it so far?

I don't do a whole lot of resampling, but when I do it sounds, well, not like any instrument. When I resample sounds I usually end up with an ambient sound. Here's what I usually do:

Take any sound. Literally anything.
Maybe distort it a little. Random effects. Stuff like that.
Now if you're using FL, take it into edison, and run it through a bunch of its blur/reverb effects. This can create some really cool ambience. I have a bunch of stuff I made that way on my Freesound: https://freesound.org/people/IanStarGem/ (will remove link on request)