LÖVE

I want to make a jet trail, but how would I do this? I don't even know where to start.

Two methods.

Make a particle system. You should be able to find code that lets you plug and play.

The harder but cooler method is to generate a polystrip using the mesh function. Which is how the slashes in a game like fruit ninja is generated.

https://love2d.org/wiki/love.graphics.newMesh

I would recommend using a particle system, which is actually very useful in LOVE.
Just look up love2d particle system on the wiki