Hi,

It seems you are asking how to add one2many fields to your model, if so please see this video explaining the same: How to Add One2many Fields In Odoo

Thanks

You can filter sale order line by sale order id many2one in your custom module.

check my working code below,

class custommodule(models.Model):
    _name = 'custom.module'

    _description = "custom module"
    sale_order_id = fields.Many2one('sale.order', index=True, required=True)
    order_lines = fields.One2many('sale.order.line', 'line_id', 'Order Lines', domain="[('order_id','=','sale_order_id.id')]")

    @api.onchange('sale_order_id')
    def onchange_sale_order_id(self):
        self.order_lines = self.sale_order_id.order_line


class mymodule_line(models.Model):
        _inherit = 'sale.order.line'
        line_id = fields.Many2one('custom.module', string='Order')