Speak can mean using a language or addressing someone formally.
- I speak English and Kiswahili.
- May I speak to the manager?
- She will speak at the conference.
Talk usually refers to conversation or informal communication.
- We talked for an hour.
- Can we talk?
- They were talking about football.
Simple guide
Speak can sound more formal or focus on language.
Talk usually suggests conversation.
There is considerable overlap between the two words.