before you will try to use {% trans %} blocktag you need to type
{% load i18n %}
then you can use the tag to type in the text you want to be translated (one thing is important - the text ought to be in main project language which is set in settings)
if you have already some text you want to translate type in your projects main dir:
./manage.py makemessages -l pl
where "pl" can by country code of the language of choice. this command will make django scripts generate a right localization file located in the ./locale/(language-code)/LC_MESSAGES/django.po.
after doing the translation stuff you simply type
./manage.py compilemessages
and that should do the trick.