We had no idea what a biological cycle was. Both of us (my husband and I) have had fish tanks before and had never even heard of it.
Science is a wonderful thing...we can now keep our fish alive for much longer and in a generally better condition. Diseases amongst those in the know are hardly ever encountered and we don't need to spend a fortune on medicines.
Growing up, my parents bred guppies and mollies and never had a fish die, save for old age and they never added anything to the water nor did they use a test kit or do weekly water changes.
Guppies are known as 'millions fish' for a reason.

That said, I'd guess the guppy life span was significantly reduced, as compared with what it could've been. In the Olden Days, fish simply living was seen as an achievement. We now know better and do better.
We just did what the guy at Pet Smart said (which is unfortunate and has caused great loss). He said to add the bacteria and a couple goldfish and wait a week before adding anything else
That guy was an idiot and should be sacked. His goal was to make money, at the expense of living creatures and your good selves. The very idea of 'a couple of goldfish' implies that he viewed those as expendable. 'Goldfish' are coldwater fish and have their own very specific needs, few of which can be provided by a tropical tank set-up. Not only has he cost you money, he's caused suffering to fish and anxiety to you and yours.
To answer your repeated question about the 'white scummy stuff'...
Without knowing about your tank size, water parameters and other fish species present (and in what numbers), I'd be guessing. It could be anything from bacteria, fungus, or, as has already been suggested, excess mucus, whilst the fish struggled to survive in toxic water.
The way forward...
- Lots of water changes, using conditioned water.
- Acquire and use a quality test kit, such as that offered by API's Master test Kit. This puts YOU in control and, believe me, any excess levels can always be reduced by something as simple as a water change.
- Having siphoned off all visible waste, fasting your fish for 24 hours wouldn't do any harm. Any future feeding should be cautious.
- Use an air pump and add aeration with an airstone or two.
- Adjust your filter to agitate the surface of the water.
- Add plants.
Since returning to the hobby, I've discovered the bottled bacterias and, from my own experience, I've been pleasantly surprised, (I use the Microbe-Lift Special Blend and Nite-Out II). That said, I cycled my well-planted tank without fish, using old gravel with an old, organic content and had fish in by week 4.