Se o prato estiver muito sujo, eu uso mais detergente e um pouco de sabão.

Because after se when you are talking about a possible future situation, Portuguese usually uses the future subjunctive.

So:

• Se o prato estiver muito sujo... = if the plate/dish is very dirty
• not Se o prato está... in this kind of conditional sentence

This is very common in Portuguese:

• Se eu tiver tempo, eu vou.
• Se ela puder, ela vem.
• Se o prato estiver sujo, eu lavo.

Even though English uses the present in if the plate is dirty, Portuguese uses the future subjunctive here.

Because this sentence sounds like a general habit or usual reaction:

• If the dish is very dirty, I use more detergent and a little soap.

So uso means something like I usually use or I use in that situation.

Portuguese often does this:

• Se chover, eu fico em casa.
• Se ele ligar, eu atendo.

If you wanted to emphasize one specific future occasion, you could say:

• Se o prato estiver muito sujo, eu usarei mais detergente.

That is grammatically correct, but a little more formal or specific.

Because sujo here is treated as a temporary condition.

• estar sujo = to be dirty right now / at the moment
• ser sujo = to be dirty by nature, character, or habit

For a dish, dirtiness is normally temporary, so estar is the natural choice:

• O prato está sujo.

If you said O prato é sujo, it would sound odd in most situations, as if the plate were somehow inherently dirty.

Because prato is masculine singular, so the adjective must agree with it:

• prato sujo
• pratos sujos
• xícara suja
• xícaras sujas

So here:

• o prato estiver muito sujo

Also, muito here means very, so it is acting as an adverb, not an adjective. As an adverb, it does not change:

• muito sujo
• muito suja
• muito sujos
• muito sujas

Compare:

• muito sujo = very dirty
• muitos pratos = many dishes

Yes. In Portuguese, the singular can be used in a generic way.

So o prato can mean:

• a specific plate/dish
• or a plate/dish in general, depending on context

This is similar to how English can say the plate in a general explanation, though English often prefers plural in some contexts.

If you wanted to talk clearly about multiple dishes, you could say:

• Se os pratos estiverem muito sujos...

But the singular version is perfectly natural for giving a general rule or describing a typical situation.

In Brazilian Portuguese, these words overlap a bit, but they are not exactly the same.

• detergente usually means dish detergent / dishwashing liquid
• sabão is soap more generally, and can refer to things like bar soap or soap products in general

So in this sentence, detergente sounds more specific, while sabão is broader.

Depending on the speaker and region, sabão may suggest a different kind of cleaning product from detergente, not just a synonym. A learner should know that detergente is the safer word for standard dishwashing liquid.

Because detergente here is being used as an uncountable substance, like water, soap, or sugar in English.

So:

• mais detergente = more detergent
• um pouco de sabão = a little soap

You do not need an article here because you are not talking about a specific bottle or unit. You are talking about quantity.

If you said something like mais do detergente, that would mean more of the detergent, referring to a specific detergent already known in the conversation.

Because um pouco de is a fixed expression meaning a little bit of.

So the pattern is:

• um pouco de água
• um pouco de açúcar
• um pouco de sabão

The de is required in standard Portuguese.

You may also hear pouco sabão, but that usually sounds more like little soap / not much soap rather than the more natural a little soap.

So in this sentence, um pouco de sabão is the most natural choice.

Yes. Portuguese often omits subject pronouns because the verb ending already shows the person.

So both are correct:

• Se o prato estiver muito sujo, uso mais detergente...
• Se o prato estiver muito sujo, eu uso mais detergente...

The version with eu may sound a bit more explicit, emphatic, or conversational. The version without eu is also very natural.

Here se means if. It introduces a condition.

The structure is:

• Se + future subjunctive, present/future result

In this sentence:

• Se o prato estiver muito sujo = the condition
• eu uso mais detergente e um pouco de sabão = the result

This is one of the most common Portuguese conditional patterns.

Yes. Portuguese allows some flexibility.

For example, you could also say:

• Eu uso mais detergente e um pouco de sabão se o prato estiver muito sujo.

That means the same thing.

Starting with Se o prato estiver muito sujo... is especially common because it presents the condition first. That order often sounds clearer and more natural when giving a rule or explaining what you do in a certain situation.