How do you send settlers for resources? (Fallout 4)

if possible, that's great, but I don't seem to have even heard of this

The maximum where you can send them is to walk between cities and make garbage common

You can make a workbench for garbage collection (or something like that, I don't remember exactly), assign a worker to it. The idea is to go to collect. I can’t check, I have a bunch of stuff stuffed into my workbench =)
upd: I looked in the game for what it’s called. resources-> miscellaneous-> garbage collection station. a little man is drawn in the requirements.

the guides say that the settlers who are free from work collect trash themselves. for the rest of the work (food, water, security) they need to be assigned

No need for water