You are trying to learn the basics here π
Please forget Xref Manager for now... it does reload external SKP files into the current Model, listing any that have changed since they were last reloaded etc...
BUT using Reload from the context-menu reloads external SKP [Components] too [just no check to see if it has changed and therefore needs to be reloaded] π
IF you have a SKP that is used as a Component within another Model, and you know that the SKP has changed then Selecting an Instance of that Component within the Model and using Reload will update it to match...
So for example you do housing developments and have 6 commonly used house types.
You make 6 separate components as individual SKP files, these are stored in a 'Library' of your house-types.
You a SKP Model for a Site A.
You load and place the houses onto the Site A as desired.
You repeat this for another Site [B] as well.
Later on you decide to change something about the style of some of your standard house types... so you edit their individual SKP files and save...
At this point the equivalent house components in your Sites' Models are 'out of date'.
But perhaps you want to leave those on Site A in the old-style - maybe they are getting built like that already !
But you'd like to use the newest version of the houses on Site B... Simply open the Site B Model and select one of the houses you'd like updating, and right-click context menu 'Reload' - the Instances of that house are now updated to be the newer one.
If you save the changes Site B now uses the newer houses...
Of course if you have [ill-advisedly] Exploded an Instance in the Site Model it is now loose geometry and cannot be reloaded !
Also if you edit a house component in the Site Model it is now going down a separate path from its original SKP in your Library... Although if you want to revert to the original Library you can Reload that back in, overwriting any Site specific changes...
OR if the changes are such that'd you'd like to include them in your 'standard' one, then you can do a context-menu 'Save_as' the changed version - either saving as anew version or overwriting the original Library version - thereby allowing you to use these SKPs in other Site Models as desired...