I'm sorry to hear about your experience! The chain stores just want to make money and they just tell us stuff that doesn't make sense so that we buy something.
First of all, to make it easier, get a bigger tank. A 10 gallon is a good size for starting, with a 20 being even better. The bigger the tank, the easier it is to keep stable parameters and the more wiggle room you have for disease and such.
As for cycling the aquarium, you have two options:
Fish-in cycling: This is putting the fish in a new tank set up (like you did unintentionally) so that they provide a source of ammonia for the beneficial bacteria (BB) to feed on and grow. Fish in cycling exposes the fish to harmful toxins in the water (ammonia, nitrite and nitrate) and can scar the fish permanently. Fish in cycling also unnecessarily stresses the fish and can kill them as well. I don't recommend this method and it sounds like you don't want to use it either.
The second method, fishless cycling, is much easier. You set up the tank, add water, filter and heater and add a source of ammonia. (you can buy household ammonia from hardware stores and use this) Another source of ammonia that some people like to use is fish food. Works just as well. Buying seeded material from fish stores or using some from a friend will help the cycle along and help you cycle very quickly. I got my 16 cycled in a week using seeded material from my 10 gallon. To find out your water parameters, you need a water testing kit. You have two options as well for this:
Freshwater Liquid Test Kit: Easy to use, accurate and even though it is expensive it is definitely worth it. I recommend the API Freshwater Liquid Master test Kit. Cheaper on Amazon than at your LFS
or chain store.
Second option, test strips: I don't recommend these at all unless you are trying to get inaccurate results. They give false information and $15 is too much to spend on inaccurate things anyway.
Now, to the whole point of the aquarium: Fish!
Some easy beginner fish for a 10 gallon are guppies, danios, barbs, platys, dwarf gouramis, and any kind of small, peaceful fish. If you go with a 20 gallon, you can o course keep bigger fish and theoretically more fish of the same species. If you go with guppies or any other kind of livebearer, make sure you get just one gender because they can and will breed like rabbits. Unless you are prepared for a whole ton of fry and have somewhere to put them all I recommend all females or all males (but be careful, males may beat each other up) And I know you probably know this already, but I'm going to say this anyway: NO GOLDFISH IN ANYTHING LESS THAN A 40 GALLON! Goldfish get big and are way too big for a 20 gallon. Also, there are 2 models of a 20 gallon: 20 high and 20 long. I would always, hands down go with a 20 long because it offers more horizontal swimming space than vertical, and vise versa for a 20 high. Most fish appreciate horizontal swimming space more than vertical anyway. Once you have the basics of fish keeping down nd you have some experience, you can get into more complicated species and more sensitive fish like German Blue Rams, Dwarf Puffers and lots of invertebrates.
I hope this helped! It really is a great hobby and once you get the hang of it it's pretty easy! Good luck and give us updates along the way!