Breakdown of Ты должен пойти в магазин и купить хлеб.
и
and
ты
you (singular)
хлеб
bread
в
in / to (direction)
Questions & Answers about Ты должен пойти в магазин и купить хлеб.
Why does the sentence use должен here, and what if I am speaking to a woman?
должен is a special word meaning "must" or "have to". It changes form to match the gender and number of the person who has the obligation. Here, it is in the masculine form, which means the "you" (ты) being spoken to is a man. If you are speaking to a woman, you must use the feminine form: Ты должна пойти...
Why do we use the perfective verb пойти instead of the basic motion verb идти?
You are instructing someone to complete a specific, one-time trip. Because the focus is on successfully completing the action (getting to the store) rather than the ongoing process of walking there, we use the perfective verb пойти after должен.
Why is the phrase в магазин rather than в магазине?
We use the preposition в with the accusative case (в магазин) when expressing motion toward a destination, like going "to the store". If you were talking about being located inside the store, you would use the prepositional case (в магазине).
The word хлеб is the direct object being bought. Why didn't its ending change?
хлеб is indeed in the accusative case here because it is the direct object of the verb купить (to buy). However, for masculine inanimate nouns (objects and things, not people or animals), the accusative form is identical to the basic dictionary (nominative) form.