Если на рубашке есть складка, я сразу достаю утюг.

Because the sentence begins with an если clause: Если на рубашке есть складка, ...

In Russian, a subordinate clause introduced by если is normally separated from the main clause with a comma.

• Если идёт дождь, мы остаёмся дома.
• Если на рубашке есть складка, я сразу достаю утюг.

This is standard punctuation.

This sentence expresses a general condition or habitual reaction:

• If there is a wrinkle on the shirt, I immediately get out the iron.

Russian often uses the present tense in both clauses for this kind of repeated, regular situation.

So:

• есть = there is
• достаю = I get out / I take out

It does not mean only what is happening right now. It can mean whenever this happens, this is what I do.

Because a wrinkle or crease is thought of as being on the surface of the shirt, not inside it.

• на рубашке = on the shirt
• в рубашке would usually mean inside the shirt or wearing a shirt, depending on context

For marks, stains, wrinkles, buttons, and similar things on clothing, Russian often uses на.

After на in the meaning of on / at a location, Russian uses the prepositional case.

• рубашка = nominative
• на рубашке = prepositional

So the ending changes:

• рубашка → рубашке

This is the normal pattern for many feminine nouns ending in -а.

Here есть means there is / there exists.

So:

• На рубашке есть складка = There is a wrinkle on the shirt

Russian often uses есть when introducing the existence of something.

It is possible in some contexts to omit есть, but here keeping it is very natural because the sentence is about the presence of a wrinkle.

Compare:

• На рубашке есть складка. = There is a wrinkle on the shirt.
• Складка на рубашке. = more like A wrinkle is on the shirt or just naming/describing it, less neutral in this context.

Складка literally means fold, crease, or wrinkle, depending on context.

In clothing, it can refer to:

• a fold in the fabric
• a crease
• a wrinkle that should be ironed out

So in this sentence, a natural English equivalent is wrinkle or crease.

Достаю comes from доставать / достать, which means to take out, to get out, or to pull out.

That works well with утюг, because the idea is probably:

• the iron is somewhere stored away
• you take it out when needed

If you said беру утюг, that would mean I take the iron, which is possible, but it sounds a bit less specific.
Достаю утюг suggests I get the iron out.

Because достаю is imperfective present, and it fits a habitual meaning:

• Whenever this happens, I get out the iron.

Russian imperfective present is often used for repeated or regular actions.

By contrast:

• достану is perfective future
• it would mean something like I will get out the iron

So:

• Если на рубашке есть складка, я сразу достаю утюг. = habitual
• Если на рубашке будет складка, я сразу достану утюг. = one future situation

It is in the accusative, but for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: утюг
• accusative: утюг

Since утюг is the direct object of достаю, it is in the accusative, but there is no visible change.

Compare with a feminine noun, where you would often see the difference more clearly:

• Я достаю рубашку.
• nominative: рубашка
• accusative: рубашку

Сразу means right away, immediately, or at once.

In this sentence:

• я сразу достаю утюг = I immediately get out the iron

Its position is fairly flexible, though some positions sound more neutral than others.

Natural options include:

• я сразу достаю утюг
• я достаю утюг сразу

The version in your sentence sounds very natural and neutral.

Yes, Russian can often omit subject pronouns when the verb ending already shows the person.

So you could say:

• Если на рубашке есть складка, сразу достаю утюг.

That is grammatically possible.

However, including я is also perfectly natural. It can make the sentence a little clearer or slightly more explicit.

So both work:

• ..., я сразу достаю утюг.
• ..., сразу достаю утюг.

Yes, in the right context it can be understood that way, but its most natural reading is habitual: whenever there is a wrinkle, I get the iron out.

Russian present tense often covers:

• what someone does regularly
• general truths
• near-future or planned action in some contexts

If you want to make the future meaning more explicit, Russian would often use future forms:

• Если на рубашке будет складка, я сразу достану утюг.

That version clearly points to a specific future case.