Если поле заполнено правильно, рядом появляется зелёная галочка.

Russian has no articles, so there is no separate word for the or a/an.

So:

• поле can mean a field or the field
• зелёная галочка can mean a green checkmark or the green checkmark

The exact meaning depends on context. In this sentence, because it sounds like a UI instruction or description, English naturally uses the field.

Because Если поле заполнено правильно is a subordinate clause introduced by если (if), and in Russian such clauses are normally separated by a comma from the main clause.

So the structure is:

• Если поле заполнено правильно, = If the field is filled in correctly,
• рядом появляется зелёная галочка. = a green checkmark appears next to it.

This comma is required in standard Russian punctuation.

Если means if. It introduces a condition.

So the sentence has the pattern:

• If X, Y
• Если X, Y

Here:

• X = поле заполнено правильно
• Y = рядом появляется зелёная галочка

It is a very common word for real or possible conditions.

Заполнено is a short passive participle from заполнить / заполнять (to fill in, to complete).

In this sentence, it works like part of the predicate and means:

• is filled in
• has been filled in
• is completed

So поле заполнено literally means something like the field is filled in.

This is different from a normal finite verb form. Russian often uses short passive participles this way to describe a resulting state.

Compare:

• Поле заполнено. = The field is filled in.
• Поле заполняют. = They are filling in the field.

Because поле is a neuter singular noun.

The short passive participle agrees with the noun in gender and number:

• masculine: заполнен
• feminine: заполнена
• neuter: заполнено
• plural: заполнены

Since поле is neuter singular, the correct form is заполнено.

Because правильно is an adverb, and it describes how the field is filled in: correctly.

• правильный / правильное = correct (adjective)
• правильно = correctly (adverb)

Here the idea is not a correct field, but rather the field has been filled in correctly.

So:

• правильное поле = a correct field (usually not what you mean)
• поле заполнено правильно = the field is filled in correctly

Появляется is the present tense of the imperfective verb появляться.

It is used here because the sentence describes a general rule, repeated behavior, or how the interface works:

• If the field is filled in correctly, a green checkmark appears next to it.

Russian often uses the present tense for this kind of general description, just like English does.

If you used появится instead, it would sound more like a single future event:

• Если поле будет заполнено правильно, рядом появится зелёная галочка. = If the field is filled in correctly, a green checkmark will appear next to it.

Both can be possible, but появляется fits a general instruction/interface behavior very well.

Рядом means nearby, next to, beside.

In this sentence, it means something like next to the field or next to it. Russian often leaves this implicit when the reference is obvious from context.

So:

• рядом появляется зелёная галочка
  = a green checkmark appears nearby / next to it

You may also see:

• рядом с полем = next to the field

Here, с полем is omitted because it is easy to understand from context.

Галочка usually means checkmark, tick, or little tick mark.

It is a diminutive form, which is very common in Russian. In interface language, галочка is a natural word for a checkmark symbol.

Depending on context, it can mean:

• a visual checkmark/tick
• sometimes a checkbox tick

In this sentence, it clearly means the little green mark that appears to show something is correct.

Because галочка is a feminine singular noun, and the adjective must agree with it.

So:

• masculine: зелёный
• feminine: зелёная
• neuter: зелёное
• plural: зелёные

Since галочка is feminine singular, the adjective is зелёная.

Also, the whole phrase is in the nominative case because it is the subject of появляется:

• зелёная галочка появляется = a green checkmark appears

Yes, Russian word order is fairly flexible, though the original version is the most neutral and natural for this context.

Original:

• Если поле заполнено правильно, рядом появляется зелёная галочка.

Possible variations:

• Если поле заполнено правильно, зелёная галочка появляется рядом.
• Зелёная галочка появляется рядом, если поле заполнено правильно.

These are understandable, but they may shift emphasis slightly.

The original sentence sounds smooth and standard because it presents:

1. the condition first
2. then the result

That is a very common pattern in Russian.

Mostly a state resulting from an action.

So поле заполнено does not focus on when someone filled it in, but on the fact that it is now in a filled-in state.

That is why it works well in this sentence:

• Если поле заполнено правильно... = If the field is filled in correctly...

The emphasis is on the current condition of the field, not on the action of filling it in as an event.