self.env.cr.execute( " Your Request here")

 result = self._cr.fetchall()

 if result:

      # Result is your datas you get from your sql request. then you define  what you want to do with it within a loop

When you write a many2many field a new table is created in the database which stores the id of the two tables. In your example, the new table created is rel1 and a will be the id of the record from table checked_criteria and b will be the id of the record from softandgrid.

For understanding the concept, the naming can be done as follows:

soft_grid_ids = fields.Many2many('softandgrid', 'criteria_softgrid_rel', 'criteria_id', 'softgrid_id', string='Soft Duplicates Fields')