K so i have no idea what an fx loop is or what the purpose is.
i have a marshall MG100DFX and on the back it has an "FX send" and "fx return".
what the difference instead of using the pedal before the amp.
i have a boss metalzone (does it do anything with distortion)
and also a digitech GNX 3.
can anyone help me understand this concept
i know i'm an effects noob so that doesnt need to be said
thank you
Here goes my description, I'll probably have some facts wrong...

Amps generally have 2 parts. PreAmp and PowerAmp

Preamp is low current going into the preamp tubes.
This is where tone(treb/mid/bass) and distortion are added to the signal from your guitar.
It's still low current, not amplified.

Then that "Colored" Signal is sent to the PowerAmp.
This is where it is amplified and made into a High current to be sent to the speaker.
some distortion is added in the PowerAmp, but only when you really have it cranked.
If you're not REALLY cranking it, the distortion is all coming from the preamp.

so to summarize, tone and distorition comes from preamp, volume comes from PowerAmp.

So the Effects loop lets you choose wheather you want your effect pedal to be added Before or after the preamp.
This is usefull because if you put say a Delay pedal BEFORE the preamp, then the preamp tubes are adding "Color" to a signal that has been delayed. This is not good.

And same for a distortion or overdrive pedal.
It is best to have those pedals BEFORE the preamp. So the distortion/od from your pedal is already in the signal from the guitar, then goes to the preamp.

It's all personal preference, which pedals you want before or after the preamp..
But in general...

These go BEFORE Preamp (direct into AMPs input jack)

These go AFTER the Preamp (in the effects loop)

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2001 MIM Standard Strat
Peavey Classic 30 112 Combo.
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