To hide the field first we have to go in .XML file (OpenERP)
After that we have to decide where we want to hide the field and then give attribute invisible to that field.
As in example below, .XMLcode in XML file : -

<record id="view_order_form" model="ir.ui.view">
    <field name="name">start.end.dates.view_order_form</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form" />
    <field name="arch" type="xml">
        <xpath expr="//field[@name='order_line']/form/group/group/field[@name='product_id']" position="after">
            <field name="start_date"
                on_change="start_end_dates_change(start_date, end_date, product_id, product_uom_qty, context)"
                attrs="{'invisible': [('must_have_dates', '=', False)], 'required': [('must_have_dates', '=', True)]}"/>
            <field name="end_date"
                on_change ="start_end_dates_change(start_date, end_date, product_id, product_uom_qty, context)"
                attrs="{'invisible': [('must_have_dates', '=', False)], 'required': [('must_have_dates', '=', True)]}"/>
            <field name="must_have_dates" invisible="1"/>
        </xpath>
    </field>
</record>