this is probably the stupidest question but
when i either right my own code
or actually type out prewritten code instead of just copying and pasting it

i get an error saying "main script not found-check prefrences"

how can i get the codes to compile

you have to save your code before you compile it

You also have to check the box "Use current script" (or similar) in the preferences of SED.
I'm not sure where exactly that option is, as I'm on a system without 3DGS at the moment.