How do you make a cleared place into a settlement?

By pure fluke i clicked on a red workbench once and found out that did something MAJOR and made it so I could now build stuff but NOWHERE did the game ever tell me this important information!

Possible Spoiler alert?

So can I make Fort Hagen Filling Station a Settlement?

It has an armour workbench, a weapon workbench and a power armour station but i can't find any red workbench to click, and holding down V produces no build menus.

Some locations can be cleared independently to create new settlements.

Some you have to be given a mission to help out existing settlers after which they join you.

Only places with a red workshop bench can be made into settlements.

The settlement building "tutorial" comes from a quest very early in the game. Unless you gain a location with existing settlers you'll have to get new ones to appear. Easiest way is to build a recruitment beacon, it's located in the power section when you're in build mode. You'll have to power it before it works. Build a power generator and hook up a wire between the beacon and the generator. Once it's operational it will attract new settlers over time. If you've got people in other settlements you can order settlers (unnamed ones) to move to your new settlement.

If you want to keep them there you'll have to build beds (under furniture), defenses (under defense), food and water (under resources). 1 bed per settler. 1 unit of water/food per settler. Defense should be equal or higher than your combined food and water. Each settler can generate up to 6 food unless you assign it to something else (like a guard post or shop).

Yeah. At times, the Red Workbench will be obvious to find.

Others, like, say County Crossing, you wouldn't even know it was there because it's 10% of a house foundation and some cars outside of the nation guard training depot. And the workbench there is hidden from view if you're coming from the road.

After you have found a place, when you select it's marker in a map the tooltip that pops in has couple extra lines for locations that are settlements (and to my knowledge, for one location that is not, but it's obvious at that point) Look at the Sanctuary map marker tooltip to see what I mean. So, if you find a place and it's map tooltip only tells the place name, then it's not a settlement location.

That is, you don't make places to be settlements. The game has preset places that have that ability, some require a bit of questing to unlock it but places that don't have the capability in the first place are no go.