rawia_tsalih,
If the dropdown displays a person's name for example it is getting it from the SQL used in the dropdown the field on the Form, actually stores the person's id,
You will see this if you look at the actual row in the database.
To display the name you must create a JOIN in the SQL of join both the table you are using and the table with the person's name.
And display the field holding the person's name not their Id, in the Browse.
http://www.w3schools.com/sql/sql_join_inner.aspSteven