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Glad to help! In this PDF you can find some of the stops with their names. Please note this is an older one. Some of those information might not be valid anymore. But anyway, in the second column you can find the boarding points - I also provide you some details regarding the abbrev. you find in this file:
SS 26 stands for: Strada Statale 26 della Valle d'Aosta (so wherever you see this I guess you should stand in the highway waiting for the passing bus?)
FS in Italy generally stands for: train station (ferrovie dello stato)
I also suggest you to install the app of the company. You can find it here. I did a sample search of your route and the result seems to be clear enough - furthermore you can directly buy the ticket from there.
As you can see in the screenshot first you should go to Bivio F.S in the Pre Saint Didier - and then from there (actually from SS 26) take another bus to Aosta - in the attached PDF I see the difference between these two (Bivio F.S && SS26) is 2 minutes by bus so I'd say it's a 5 minutes walk.