Ok, let me explain, You cannot pack a pack with another first unpack one of them then pack it with another.
For using collections, first go to Main Page at top of it it has Button called Collections, click it then in Collection page make a collection name it what ever you want, then right-click on a downloaded post > collections > add post to any collection you created.
Now for random button, its not for randomizing Images or stuffs its for randomly pick a page and open it, ex. you have 100 page its will randomly open page between 1 to 100; and if you say it does not do anything that mean you only have 1 or 2 page.