Starting from your Sales & Orders account:
Navigate to the Feed Tool>Feeds
Scroll down to File Feeds
If you don't have your Snapchat catalog created yet, select it from the drop down menu and then click Generate files. Please allow for anywhere from 5 minutes or more to have the file generated
IMPORTANT: Snapchat will accept a CSV or TXT file so be sure to copy only one file type once your catalog/feed has been generated.
From Snapchat Ads Manager:
Log in to Ads Manager
Click the menu in the top corner and select Catalogs
Select Use Product Feed
Name your catalog
Paste the catalog/feed file URL generated by Sales & Orders into the field designated under Add Products
Note that S&O file URLs are NOT password protected
Set your Update Schedule for how often and when you'd like Snapchat to fetch your feed
Attach Pixel(s) to your Catalog (required for Dynamic Ads)
Invite staff to manage your Catalog (not required)
Click OK to finish up
Now, with your Catalog created, you can review diagnostics and even edit the Catalog settings in Snapchat Ads Manager > Catalogs.