create a new php document in Dreamweaver.
Go to Insert -> Form -> Form to create the form.
Go to Insert -> Form -> File Filed to add a file field to the form.
go to Insert -> Form -> Button to add a submit button to the form.
Now go to Insert -> WebAssist -> File Manipulation -> Upload file to add the file upload server behavior.
in the upload server behavior click the help button for more details on tjhe various settings.