How to Identify a Fraudulent Email Letter ?

Hi Experts!
I've been receiving a lot of emails on a daily basis. Most of it comes from unknown sender. What I want to know is, how can I identify if the email is a fraudulent email or not? The question may seem to be very common to ask, but believe me I am getting confused on which one on my inbox is fraudulent or not. How can I stop it from sending me emails? I need advices. Thanks.
