i have all kinds of junk i keep storeing in the workshop how do i break down some of that junk to get what i need

It happens automatically when whatever you are crafting needs a component within an item.

If it's in the workshop inventory, it just breaks it down automatically as you craft mods and settlement components. Any unused materials will be returned to the workshop inventory.

Yeah, you don't need to it takes care of it when you need to make something.

If you anol like me though you'll dump everything out of you pockets at the front of the red rocket and break it all down via the workshop build control.

what about settlements are these important can i only have to build one?

you can steamroll through the game without giving a flying frickin fricks about settlements
however, you'll find that Big Sale and Local Leader + settlements and shops makes for incredibly fast bottlecap farming