Learn Polish: Wczoraj trzeba było przynieść starocie na targ. - Yesterday it was necessary to bring the old things to the market.

Trzeba było is the past tense of the impersonal modal trzeba (it is necessary). Because it is impersonal, the sentence doesn't specify who had to bring the old things. It simply states that the action was necessary in general. If you wanted to specify a person, you would typically use a personal verb instead, like musieliśmy (we had to).

Could I use the imperfective przynosić instead of the perfective przynieść after trzeba było?

You could, but it changes the context. The perfective przynieść focuses on completing the action for this specific event yesterday. If you used the imperfective przynosić, it would usually imply a repeated, habitual necessity, like saying 'Back in the day, it was always necessary to bring old things.'

The word starocie means 'old things'. What is its singular form and what case is it in here?

The singular form is staroć, which is a masculine inanimate noun meaning an antique or an old piece of junk. Here, starocie is in the accusative plural because it is the direct object of the verb przynieść.

Why do we use na targ (accusative) instead of the locative case na targu?