Learn Spanish (Spain): ¿Tienes que comprar la sal ahora?

In Spanish, the phrase tener que means "to have to" do something. If you leave out que, the verb tener just means "to own" or "to possess". So tienes que comprar means "you have to buy", while tienes sal would mean "you have salt".

Why is comprar in its dictionary form instead of ending in an "s" for "you"?

When two verbs go together to form a single idea, you only change (conjugate) the first one. Here, tienes is changed to match "you". The second verb, comprar (to buy), stays in its full dictionary form (the infinitive).

Why is it la sal instead of el sal?

The word sal (salt) is a feminine noun in Spanish, which is why it uses la. Because it doesn't end in a typical feminine "-a" or masculine "-o", its gender is simply something you have to memorize.

Where is the word for "Do" in the Spanish sentence?

Spanish doesn't use helper words like "do" or "does" to make questions. You simply take the normal statement (Tienes que comprar la sal ahora meaning "You have to buy the salt now") and add question marks and a questioning tone of voice!