Hi Fishcoop.
Okay, sounds like you have a 2 gallon tank with an air bubbler. That is not a filter. Thing is that without a filter you will have to change the water in your tank and clean the gravel every day or two. If you get a filter, which sucks water through a system of sponges and other materials and then puts back clean water, will let you get away with cleaning the tank once a week. You see, your fish and frog, poop and pee and that raises ammonia levels in the water which will kill the fish and the frog. I'm guessing the frog is more sensitive. It is like if you had to live face down in your toilet, you wouldn't last long. So you have to clean it up for them. The filter will do part of that for you but you still have to clean once a week.
Now with a goldfish, you should know that it will eventually outgrow that tank. Goldfish grow huge, so with the goldfish and the frog, you have no more room in the tank for more fish. You have to look at how big they will get not how big they are now.
The last thing is that goldfish are a cold water fish and don't need a heater. Almost all your other aquarium fish need a heater. I'm not sure about your frog. He may need a heater so you better check that out. Many fish and frogs can't survive in unheated water.
Check the web for fish tank filters to get an idea of what is out there and what they look like.
Hope this answers some of your questions.