Not the best place to put this question should be under general revit

However understanding shared parameters requires more than basic revit knowledge

Have you ever used the family editor?

Do u know the difference between type, instance, shared, & project parameters?

Simply put, shared parameters are kept in a text file. You can load them into families easily. This allows you to have a central location where all of your parameters are located so there is never a doubt that the syntax, spelling, etc. are 100% consistent.

Basically a shared parameter can be scheduled and show up in a tag and is kept in a unique file so that they can be "reused" by selecting them from the file. So in your example you download 3 diff. mfr chairs. Each has a "project parameter" for the width of the chair. one is called Chair width, one is just W, and one is Width. You won't be able to schedule the width of these chairs because the parameter is diff. for each MFR(why we need a standard, diff. story). What you need to do to solve your problem is create a shared parameter for the width of chairs. Lets call it "Furn_Width_Common" or whatever you want it called. Now you need to open all the content you want to have the width scheduled and swap out the width "project parameter" in each family with your shared parameter "Furn_Width_Common". or you can just add that parameter to all your content and set the project parameter to equal this shared parameter. Once you have all your content "sharing" the same parameters, you will be able to schedule them.

One things new users struggle with a lot is that Revit will let you have two DIFFERENT parameters that have the same name.
Similar to Scott's example above, let's say you create a Chair family that uses a parameter named "HasArms"
Next you make another new Chair family, and add a new parameter to it named "Has Arms".
Those are NOT the same parameter. You'll find that, once you load both families into a Project, you'll see two "Has Arms" parameters when you try to schedule them.
That's because Revit - behind the scenes - doesn't use the name. Behind the scenes, Revit uses what's called a GUID (Globally Unique IDentifier).
The "Unique" is the gotcha there. Every Parameter that Revit creates is unique - regardless of the name.
That's where the Shared Parameter File (SPF) comes in.
The SPF stores those GUIDs so that each time you create a family, you can add that "HasArms" parameter from the SPF, and it WILL be that same parameter for every family

I have previously used the family editor.
I understand that the difference between a type and an instance is that setting the parameter to Type means it applies to the entire family whereas Instance applies to each separate item. Project parameters are specific to the project and cannot be shared with other projects. And a shared parameter can be used in multiple families or projects and it protected from change in a separate file. Is this all a decent definition of those things?

Thank you very much for your explanation.
This might be a stupid question but could you please just explain why using shared parameters is more beneficial and how this is going to help our workflow?
I understand that scheduling is very important for pricing and organizing a project, shared parameters are useful for that, but is this the only benefit?

If you want to Tag your families, you will NEED a SP to define the parameter that the Tag uses.
Also (as I found out the hared way), if you define a parameter in a family, and then swap out that family with a different one, if you don't use a SP, the values will not transfer to the new family.

And finally, your description in post #6 is close, but not quite.
Not the entire family, but the entire Type within that family.