Se faltar óleo, você pode usar manteiga para fritar o alho.

After se when talking about a possible future situation, Portuguese normally uses the future subjunctive. For regular -ar verbs, that form looks exactly like the infinitive, so faltar here is not just the dictionary form showing up randomly; it is the correct verb form for this structure.

That is why Portuguese says:

Se faltar óleo...

Compare with irregular verbs, where you can see the pattern more clearly:

• Se tiver tempo...
• Se puder...
• Se for necessário...

The subject is óleo.

That can feel strange to English speakers, because English often says if you run out of oil. But Portuguese faltar often works more like to be lacking. So the structure is closer to:

if oil is lacking

That is why óleo is the thing connected directly to faltar.

Yes. Se não tiver óleo is very natural in Brazilian Portuguese.

There is a small nuance:

• Se faltar óleo = if oil is lacking / if you run short of oil
• Se não tiver óleo = if there is no oil / if you do not have oil

In everyday speech, both can work in many of the same situations.

Because both are being mentioned in a general, non-specific way.

In Portuguese, ingredients and substances are often used without an article when speaking generally, especially in recipe or advice style:

• usar manteiga
• comprar pão
• precisar de água

So óleo here means oil in general, and manteiga means butter in general.

If you wanted to refer to specific oil or specific butter already known in the conversation, an article could appear.

Portuguese often uses definite articles with ingredients or objects involved in the situation:

• corte a cebola
• frite o alho
• lave o arroz

So o alho means the garlic relevant to the recipe or context. It does not mean all garlic in the world; it means the garlic you are working with.

Not always.

Portuguese often leaves subject pronouns out when the context is clear. So this is also possible:

Se faltar óleo, pode usar manteiga para fritar o alho.

However, pode by itself can mean you can, he/she can, or even a more general one can, depending on context. Adding você makes it explicitly directed at you.

Here it mainly expresses practical possibility or suggestion.

So você pode usar manteiga means something like:

you can use butter or butter is an option

It is not really formal permission, like a teacher saying you may do something. It sounds more like helpful advice.

Para introduces purpose.

So usar manteiga para fritar o alho means use butter for the purpose of frying the garlic.

It explains what the butter is for.

Yes. In Brazilian Portuguese, pra is extremely common in speech and informal writing.

So these both work:

• para fritar
• pra fritar

In more careful or formal writing, para is preferred.

Not necessarily. Alho often means garlic as an ingredient in general.

If you want to specify clove of garlic, Portuguese usually says dente de alho.

So:

• alho = garlic
• um dente de alho = one clove of garlic
• dois dentes de alho = two cloves of garlic

Usually not.

In Brazilian Portuguese:

• óleo usually means cooking oil such as soybean oil, corn oil, sunflower oil, etc.
• azeite usually means olive oil

So if you specifically mean olive oil, azeite is the more precise word.

Yes, and all of them can sound natural, but they are slightly different.

• Se faltar óleo = if oil is lacking / if you are short on oil
• Se acabar o óleo = if the oil runs out / gets used up
• Se ficar sem óleo = if you end up without oil

So faltar is a bit broader, while acabar and ficar sem are often more specific about running out.

Because Se faltar óleo is a conditional clause placed before the main clause.

Portuguese normally separates that kind of introductory clause with a comma:

Se faltar óleo, você pode usar manteiga para fritar o alho.

If you reverse the order, the comma is often not used:

Você pode usar manteiga para fritar o alho se faltar óleo.