It was an election to elect councillors for the council in your local constituency. It was a run of the mill election, that took pace across the whole of the UK, with schools or village halls etc being used as polling stations just like always; but the government were trying out postal voting and some other methods just to decrease voter apathy and get more people to vote.
The reason that you didn't receive any polling cards and didn't see your polling station open (unless you're looking at the wrong school or you're not on the electoral register) is because elections were only taking place in some wards/parishes and not all, it simply depended on whether any political party was fielding opposition to your parish council. Hope that answered your question Essex girl