If i want to pop out a message to user
eg, please enter number only.
Do i need to declare? If need, how do i declare.
My test is in 2 days time.
Thanks in advance.

Dim string msgbox("please enter Numbers only!")
am i correct.

No you are not correct. You have already been given the answer....

If you want an inputbox where the user enters the input into the messagebox, then you do have to assign the return value to a string variable. But as Sknake say above, its not needed if it is only displaying a message.