Hi!!!
"Tudo bom" and "Tudo bem" you can say when you will ask someone how is he, and use both as a question or an answer, for example:
- Tudo bom?
- Tudo bem.
- Tudo bem?
- Tudo bom.
The difference is that "Tudo bem" you can use in a general way too.
Question Example: How was your day?
- Como foi o seu dia?
- Foi tudo bem!
If you need more explanations, please ask me!!!
Cheers,
Ali