Если рана маленькая, её заклеивают пластырем.

Because маленькая has to agree with рана.

• рана is feminine, singular, nominative
• the adjective маленький changes to match it
• so маленький → маленькая

This is normal Russian adjective agreement: adjectives match the noun in gender, number, and case.

Because её is the form used for a direct object here.

• она = she/it as the subject
• её = her/it as the object

In this sentence, the wound is not doing the action; the wound is the thing being covered. So Russian uses её.

Compare:

• Она маленькая. = It is small.
• Её заклеивают пластырем. = They cover it with a plaster.

Заклеивают comes from заклеивать. The basic idea is to stick something over / to seal or cover by sticking.

With пластырем, it means something like:

• to cover with a plaster
• to put a plaster over it
• to seal it with a bandage/plaster

So it is more specific than a general verb like лечат (treat).

This is a very common Russian pattern.

Russian often uses 3rd person plural with no stated subject to mean:

• people generally do this
• they do this
• one does this
• this is done

So её заклеивают пластырем does not mean some specific group of people. It means something like:

• they cover it with a plaster
• it is covered with a plaster
• one covers it with a plaster

This is a natural way to express a general procedure or typical action.

Because the sentence describes a general rule or usual practice, not one single completed event.

• если рана маленькая = whenever the wound is small
• её заклеивают пластырем = that is what people usually do

Russian often uses the present tense of an imperfective verb for habitual or general statements.

If you were talking about a single future situation, you might get something like:

• Если рана будет маленькая, её заклеят пластырем.

That would sound more like If the wound is small, they will cover it with a plaster.

Because Russian often uses the instrumental case for the means, tool, or material used to do something.

Here, the plaster is the thing used to cover the wound.

So:

• пластырь = nominative
• пластырем = instrumental singular

The idea is roughly:

• cover it with a plaster

This use of the instrumental is very common.

The dictionary form is пластырь.

Its forms here are:

• пластырь = nominative singular
• пластырем = instrumental singular

So if you look it up, search for пластырь.

In medical everyday Russian, пластырь usually means an adhesive plaster / sticking plaster / Band-Aid-type plaster.

So although the English word plaster can be confusing, in this context it clearly refers to the medical item, not building material.

You may also see the fuller word лейкопластырь, but пластырь is very common in normal speech.

Because Если рана маленькая is a subordinate clause introduced by если (if).

Russian normally separates subordinate clauses from the main clause with a comma.

So:

• Если рана маленькая, её заклеивают пластырем.

If you reverse the order, you still need a comma:

• Её заклеивают пластырем, если рана маленькая.

Yes. Russian word order is more flexible than English word order.

The version here is neutral and natural:

• Если рана маленькая, её заклеивают пластырем.

You could also say:

• Её заклеивают пластырем, если рана маленькая.

That still means the same thing, though the emphasis may shift slightly.

Russian relies a lot on case endings and verb forms, so word order is often used more for focus and style than for basic grammar.

Её is pronounced roughly like ye-YO, with the stress on the second syllable.

In careful writing, the correct spelling is её with ё.

In everyday typing, many native speakers write ее instead of её, but they still mean the same word. Learners should remember that the correct form in this sentence is её.

Yes, depending on context, but grammatically the Russian word here is simply рана.

It is a general word meaning wound. In everyday English, a small рана might sometimes be translated more naturally as:

• cut
• small wound
• minor wound

But the Russian grammar of the sentence stays the same regardless of which English wording sounds best in context.