Not stupid, I can see how this can be confusing if you do not know what all the pieces are in this mess.
Quick breakdown - in SmartThings world there are users and locations(hubs). When you get your first hub, you create one of each - your “user” account (username/password - lets call this U) and a location (hub, lets call this H1). So far so good and relatively simple.
Then you get a second hub for another location - you just add it to your user account U as location 2 (lets call it H2) - Now U sees all the devices in both H and H2. Still pretty simple.
But say the at the location H1 you have your spouse, who you want to be able to use the app to control devices. SmartThings thought this through, since you are never supposed to share accounts, they allow your spouse to create their own account (lets call it S) and let you “invite” your spouse to control H1. Interesting bit here is that since you only invited S to control H1, they do not see any devices in H2.
In effect what we have here is what is referred to as a “many to many” relationship between users and locations - i.e. each user can have access to many locations, and each location can have multiple users controlling it. We will exploit this in a second for our needs.
Then you add an Alexa setup, and all hell breaks loose. Alexa, by its nature is really meant to be only in one location. But when you connect SmartThings to Alexa, you connect the Alexa service to a user, not to location - so if you add Alexa SmartThings Skill and configure it using account U - it will see all the devices user U sees - which means all the devices in H1 AND all the devices in H2. This is likely not what you want, as when you are at H1 and say something like “All lights on” - you do not want all lights in H2 to go on. Furthermore, H1 and H2 may both have similar device names (say “Living Room Lights”) - which will get extra confusing for Alexa.
But the solution to this is in the SmartThings ability to have multiple accounts. So, you create a new user account we will call A1, similar to your S account, and then invite it/link it to location H1 and then configure Alexa Skill in H1 to use that account. A1 only sees devices in H1 - so when you ask Alexa to turn on all the lights, only lights in H1 turn on and when you ask it to turn on “Living Room Light” - it will not try to turn on living room light in H2 as it has no ability to do so. If you want H2 to have its own Alexa setup, then all you have to do is create account “A2” and invite it only to H2
Does this make sense?
There is one important catch here - there is an implicit assumption that the two location’s Alexa setups are not using the same Amazon account. As far as I know, a single amazon account can only handle one location and once skill configuration, so you cannot have different skills on different Alexa devices linked to the same account.
HTH
P.S. I edited the original instructions to be a little bit more clear - hopefully that will help too