Hoy voy a comprar harina y levadura para hacer pan.

Voy a + infinitive is the very common near-future structure in Spanish, like English be going to.

• voy = I go (present of ir)
• a = to
• comprar = to buy
  So hoy voy a comprar… = today I’m going to buy…
  It’s not the simple future tense (that would be compraré), but it often expresses the same idea with a slightly more immediate/plan-like feel.

Yes. Hoy compraré… is grammatically correct and means Today I will buy….
Typical nuance:

• voy a comprar: sounds like a plan/intent already formed (very common in everyday speech)
• compraré: can sound a bit more formal, definite, or “future” in tone (also used for predictions: I guess I’ll buy…)

Because the structure ir a + infinitive requires a. You can’t normally drop it.

• Correct: voy a comprar
• Incorrect: voy comprar
  Think of it as one unit: ir a
  • verb.

In Spanish, when you talk about buying some quantity of an uncountable ingredient in a general way, it’s very common to omit the article: comprar harina y levadura = buy (some) flour and yeast.
You can use articles, but it changes the feel:

• comprar harina: general, ingredient shopping
• comprar la harina: the flour (specific flour already known/mentioned, or a particular one you have in mind)

Yes: la harina, la levadura are feminine nouns.
Clues:

• Many nouns ending in -a are feminine (like levadura), though there are exceptions.
• harina ends in -a and is feminine too.
  If you add adjectives, they agree: harina blanca, levadura fresca.

Typical Spain (Castilian) pronunciation:

• harina: the h is silent → roughly a-REE-na
• levadura: roughly le-va-DOO-ra
  Also, in much of Spain, d between vowels is soft (like a quick “th” sound in this), so -dura can sound a bit like -DHOO-ra.

para + infinitive expresses purpose: in order to / to.
So para hacer pan = to make bread / in order to make bread.
Spanish often uses an infinitive (not to + verb with a subject) after prepositions:

• para hacer (not para hago)
  It’s normal to have comprar and then hacer because one action is for the purpose of the other.

You can, but the natural collocation is hacer pan for make bread (meaning the whole process).

• hornear pan means specifically to bake bread (the oven step).
• cocinar pan sounds less natural because cocinar is a broad “cook” verb and bread isn’t typically described that way.

It can move. Spanish word order is flexible, and you can reposition hoy for emphasis:

• Hoy voy a comprar… (neutral/common)
• Voy a comprar hoy harina y levadura… (emphasis on today or contrast with other days)
• Voy hoy a comprar… (also possible; a bit more literary/marked)

Normally y = and. It changes to e before words starting with an i sound (to avoid two similar sounds in a row):

• harina y levadura (normal y)
• harina e ingredientes (because ingredientes starts with an i sound)
  Note: it’s about the sound, not the letter—y stays before hierro (sounds like ye-), for example.

Common options:

• voy a comprar harina (already implies “some flour”)
• voy a comprar un poco de harina = a bit of flour
• voy a comprar un kilo de harina = a kilo of flour
• voy a comprar levadura (general)
• voy a comprar un sobre de levadura = a packet/sachet of yeast
• voy a comprar levadura fresca / levadura seca = fresh / dry yeast