I know this is a stupid question, but I’ve spent two hours on this. I know I can use the $_ to select the current object in the pipeline, but I don’t know how to select a file object in a given folder and then get it’s members. for example I have a file named foo.txt and want to access it’s extension property.
I can do (ls foo.txt).extension, but was wondering if there’s another, more direct way.
seems you have already found the most direct way 
if you can access the current object in the pipeline with $_ then that represents the file object but you dont need to use $_ for file objects
ls | select-object *
ls | select Name,Extension
this will get all the file objects in the current directory. If you are looking for a specific file then you can use -filter or where-object
ls -filter myfile | select *