Tell someone to do something
Please tell Crissy to clean up her room.
Could you tell Bob to call me?
Tell him not to do that.

Tell someone some information
Can you tell them (that) the party starts at nine?
Please tell Mr. Hopkins (that) I will be late.

Ask someone to do something
Please ask Teresa to give me a call.
Could you ask Russell to be here at five?

Ask someone for some information (Yes or No)
Ask Paula if she is coming to the party.
Could you ask them if they did the homework?
Please ask her whether she finished the assignment.

Ask someone for some information (Open ended)
Ask Randy what he is doing.
Please ask her when she will be here.
Would you ask him what he wants?
Will you ask them how much it costs?