OK. You're running a 1gal tank. It takes skill to cycle and maintain the cycle. Don't worry about it. When you have more experience, it will make sense to you. Don't overload yourself with information that's not yet useful. Don't bother with a filter for a 1 gal. Another unnecessary complication for a new keeper.
A twice-a-week water change is barely sufficient for a 1gal tank; every other day will keep your fish healthier. Try to match the refill water temperature. Get an in-tank thermometer (a few dollars)
Get Prime water conditioner when yours runs out. It helps keep ammonia down.
I'm glad you understand the importance of a heater. Good quality pellets (meat is the first ingredient) and water conditioner are important, too.
Read the stickies on Betta care at the top of this Betta Care section.
Welcome to the forum.