Could someone give me the right formula please, I'm really stuck

I would need to have an Excel file work like this :

Page 1 - column 1 : empty at the moment, but as soon as I start writing in
it I would like to have automatically some data's on 2 other sheets of the
file.

For instance :

Page 1 - column 1 :

John
Mike
John
Mike
Anna
Anna

As soon as I start typing that, I would like to have automatically on sheet
2 - column E for instance all the John's, on sheet 3 - column E : all the
Anna's aso

Can anybody help me composing the right formula for this ?  I admit I'm not
yet very expertised in Excel, but learning every day.  Thanks in advance
Momo