“Tell me a bit about yourself.”

You're interviewing a candidate for a job. You want to hear some general information about him. You say:

Tell me a bit about yourself.

Tell me a bit about yourself.

This is a common first question in job interviews in English. An interviewer asks this to get general information from the job applicant.

If an interviewer says this to you in an interview, you should answer by telling them:

• your name (if they haven't already heard or read it)
• a short history of your most recent jobs
• why you want to work at this company

...and so on. 

This is always a tough question to answer, even for native English speakers!

Tell me (something)

You can ask for information from a person this way.

"Tell me ___" is very direct, so you should probably use it when you're in a more powerful position than the person you're talking to. For example, a police officer can say to the witness of a crime:

Tell me what happened.

A teacher can say to a misbehaving student:

Tell me why you did this.

If you're not in a position of authority, you should find a more indirect way to ask for information.