koko de ugaisite kudasai.

ここ means here.

The particle で marks the place where an action happens. So:

• ここ = here
• ここで = here / at this place, for doing something

In this sentence, the action is うがいして, so で shows that this is the location where you should do it.

A helpful comparison:

• ここに = here, to here, at here (depending on context)
• ここで = here, where an action takes place

So ここでうがいしてください means Please do the gargling/rinsing here.

うがい usually means gargling or rinsing your mouth/throat.

In Japanese, it often refers to the common health habit of washing out the mouth or gargling, especially after coming home. Depending on context, English translations can be:

• gargle
• rinse your mouth
• rinse out your mouth/throat

So the exact English wording may vary, but the Japanese idea is the same.

By itself, うがい is a noun, but it is very commonly used with する to make a verb:

• うがいする = to gargle / to rinse one’s mouth

In your sentence, that する verb is being put into the て-form:

• うがいする
• うがいして

Then it combines with ください:

• うがいしてください = please gargle / please rinse your mouth

So even though うがい looks like a standalone word, the full verb idea here is really うがいする.

Because ください usually comes after the て-form of a verb.

The pattern is:

• verb て-form + ください = please do ...

Since the verb is うがいする, its て-form is:

• する → して

So:

• うがいする = to gargle
• うがいして = gargle and...
• うがいしてください = please gargle

That is why して appears here instead of する.

Good question. うがいをしてください is also possible.

With many noun + する expressions, Japanese often omits を, especially in everyday speech or simple instructions. So both of these are natural:

• うがいしてください
• うがいをしてください

The version without を is very common and sounds smooth and natural.

So:

• うがいする = common dictionary form
• うがいをする = also possible
• うがいしてください = very natural
• うがいをしてください = also correct

～てください is a polite request. It is very common in:

• instructions
• signs
• announcements
• hospitals/clinics
• classrooms
• workplaces

So ここでうがいしてください is polite, but it is also fairly direct in the sense that it is an instruction.

It is not rude. It is just standard, practical Japanese.

Softer alternatives exist, such as:

• ここでうがいしてくださいね = Please gargle here, okay?
• ここでうがいをお願いします = Please rinse/gargle here

But ～てください is completely normal.

Normally, no. ここで is the natural choice.

That is because で marks the place where an action is performed.

Since うがいする is an action, Japanese uses で:

• ここでうがいしてください = Please do the gargling here

Using に would sound unnatural here because に is not the usual particle for the location of this kind of action.

A simple way to remember it:

• で = where something happens
• に = destination, existence, specific target point, etc.

Japanese often leaves out subjects and objects when they are obvious from context.

In this sentence, the speaker is clearly talking to the listener, so Japanese does not need to say you.

English often needs the subject or at least implies it strongly:

• Please gargle here
• Please rinse your mouth here

Japanese just says:

• ここでうがいしてください

The understood meaning is Please do it here.

Japanese normally does not use spaces between words in ordinary writing. So the usual way to write this would be:

ここでうがいしてください。

The spaced version is probably for learners, children, or readability.

As for the hiragana:

• ここ is normally written in hiragana.
• うがい is very often written in hiragana.
• して and ください are also usually written in hiragana.

There are rare or technical kanji related to うがい, but in normal everyday Japanese, hiragana is much more common.

Yes. That depends on context.

うがい often gets translated as gargling, but in practical English, sometimes rinse your mouth sounds more natural, especially in places like:

• a dentist’s office
• a clinic
• a sink area

So both can be reasonable translations depending on the situation.

The Japanese word covers the general idea of washing/rinsing the mouth or throat, so the exact English wording may shift a little.

The plain form is うがいする.

Here is the breakdown:

• うがいする = plain/dictionary form
• うがいして = て-form
• うがいしてください = polite request

So if you want to learn the base verb from this sentence, it is:

うがいする = to gargle / to rinse one’s mouth