Help, one of my guppies died today.?

I'm bad with fish. I have one guppy left, can I just put it in a bowl without a filter? Will it do better than a small aquarium? I need advice on how to care for them. The guy at Petco told me to feed it twice a day some tetra pellets I got, to change out half the water once a week, etc. That's about it. Not sure what I'm doing.