1. Many2one : Store a relation against a co-model:

                arel_id = fields.Many2one('res.users')

                arel_id = fields.Many2one(comodel_name='res.users')

                an_other_rel_id = fields.Many2one(comodel_name='res.partner', delegate=True)

                

2. One2many : Store a relation against many rows of co-model:

arel_ids = fields.One2many('res.users', 'rel_id')

arel_ids = fields.One2many(comodel_name='res.users', inverse_name='rel_id')

3. Many2many : Store a relation against many2many rows of co-model:

arel_ids = fields.Many2many('res.users')

arel_ids = fields.Many2many(comodel_name='res.users', relation='table_name', column1='col_name', column2='other_col_name')