You should either buy a book on keeping freshwater fish or better yet go to the library and check some books out for free. You can also use the internet to gather a lot of information on tropical fish in general and specific information on betas. Salt is now the only treatment I use for my fish and I usually get it from the supermarket.
There is no reason to give up so soon on fish keeping...just slow down. While you are learning let your tank run with the fish you have and when you treat fish with salt DO NOT add it to your tank... treat the fish in a separate container. Just dip them in salt water for a few seconds and let them loose in your tank. You can google that also.
I had some trouble with my catfish pond early last year and treated a few catfish with salt water.
I also find it helpful to learn about where the fish come from. The climate, the water temperature, water PH. etc.
I don't know a lot about a beta but I have been keeping fish for a long time.
Politicalcenter gave you great advice. Don't stop because you lose your first few fish! We've all experienced this. I remember my first tank.....over treated it with plant chemicals and killed off most of the fish. I remember losing tons of fish to ich, fungal infections, tumorous growths, over feeding, stress, nippy fish, etc. Don't give up! You will pull through! In the meanwhile, don't add anything to the water. Let it settle by itself, then, when the tanks are safe and ready, order more fish. Don't let these small setbacks stop you from continuing with fish! Give thanks to these fish who lost their lives as you learned, learn from your mistakes, and continue on. You can do it! You're a very smart, rational, and excited young person. Your passion for fish is something I wish I saw more often in the new generations. Now off my soapbox. Good luck!