I want to sort categories e.g. alphabetically. I haven't understood how to do this. Who would provide full instructions?

Thanks for your answer but it doesn't work. Indeed, it's not possible to click on the title "name".

Do you see another solution ? I think I have to modify something in a js file.

You need to modify the action and sort by the name, write a small module, like this:

product.py file below from openerp.osv import osv

class product_category(osv.osv):

_inherit = "product.category"
def search(self, cr, uid, args, offset=0, limit=None, order=None, context=None, count=False):
    if context is None:
        context = {}
    if context and context.get('order_name', False):
        order = 'name'
    return super(product_category, self).search(cr, uid, args, offset=offset, limit=limit, order=order, context=context, count=count)

product_category()

XML - product_view.xml <openerp> <data> <record id="product.product_category_action" model="ir.actions.act_window"> <field name="context">{'order_name':True}</field> </record>

</data>

</openerp>