How do delay lines create so many effects?
A DSP / Audio delay line doesnt create any effect in itself, a delay is simply a timed delay in the signal. it has no sound difference, it repeats the sound once and mixes it over original or sends it to a different mix line.

A feedback delay repeats the sound multiple times at the delay interval frequency, it sounds like a digital echo, and can become an oscillator above 20hz. almost all fx delays use variable feedback controls to control the number of repetitions of a sound, and they are filtered out as they feed back therefore diminishing.

Modern delays can work like grain synth samplers and often are based on them which have integrated effects like pitch shifting and research Grain-Delay and Grain-Resampling for infor about that. Squarepusher is somneone who uses alot of grain delay sometimes...

So a delay in effect is barealy an effect, but it can become an osciallator, has complex variants, and can feed into other lines that have any kind of additional FX.

To get a firmer grasp of that program i foudn this vid was more informative:

https://www.youtube.com/watch?v=ySzjFU6J4Ck

it's a pretty simple and very well balanced grain-delay with good controls and some bit crushing types of FX, and probably some filters too.