Welcome to TFF Claire!
The single most urgent thing for you to be doing while you seek advice here is to learn the proper skills of water changes and be performing them for your goldfish.
I would suggest at least 50% water changes daily, starting immediately, until you can learn about and acquire the proper water testing kit and give us feedback about your test results.
To water change, you siphon or dip the water out (later you will learn the skill of gravel cleaning during this water removal) and then you prepare the replacement water. The replacement water should (we'll assume for now your tap/source water is good!) be adjusted to roughly the same temperature (by just using your skin to roughly judge - that's good enough) and its very important that you add a conditioner to remove the chlorine or chloramines from it (you must pick this up at LFS if you don't already have.) Be sure to use enough conditioner, doesn't matter if it is slightly higher.. won't hurt anything.
OK, that's the first urgent thing, the water changes. Let us know you've absorbed that and the members will continue to help you. Long term, I'm afraid I have to agree that the advice will probably be disconcerting - I believe the goldfish folks often recommend 20 US Gallons for the first goldfish and 10 more US Gallons for each added one (learning this, one quickly sees why they are often more recommended as pond fish! But there is a forum of goldfish fanciers here, so they will have much more interesting viewpoints!)
~~waterdrop~~