x = fields.Many2one(model_name, string)

In view

<field name="x"/>

This will give the dropdown on view with create and edit option of the related model and display the rec_name of each entries. If you need the pure selection list as a widget selection with the field.

<field name="x" widget="selection"/>

These are the params we use while creating many2one field.

Next is you can use the Selection.

here you can specify values directly as a key value pair.

x = fields.Selection([
        ('normal', 'In Progress'),
        ('done', 'Ready for next stage'), 
        ('blocked', 'Blocked')], string='State')