Remojo la ropa en agua fría.

Remojo is the yo form of the verb remojar in the present indicative.

• remojar = to soak
• remojo = I soak / I am soaking

So the verb ending -o tells you the subject is I.

Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

• Remojo already means I soak
• Yo remojo is possible, but usually unnecessary

You might include yo for emphasis, contrast, or clarity:

• Yo remojo la ropa, pero tú la lavas.
  = I soak the clothes, but you wash them.

In Spanish, ropa is usually a singular collective noun. Even though English often says clothes, Spanish commonly uses singular ropa to mean clothing in general.

• la ropa = clothes / clothing

So la ropa is the normal way to say the clothes in most everyday situations.

Spanish uses articles more often than English does. Here, la marks ropa as the direct object and sounds natural in standard Spanish.

• Remojo la ropa = I soak the clothes

Without the article, Remojo ropa, the sentence sounds less natural in most contexts unless you are speaking very generally or in a shortened style.

Here en means in. It shows what the clothes are being soaked in.

• Remojo la ropa en agua fría = I soak the clothes in cold water

This is a very natural choice with remojar.

If you said con agua fría, that would mean more like with cold water, which is possible in some contexts, but en fits the idea of soaking more directly.

Spanish often leaves out the article when talking about a substance in a general way.

• en agua fría = in cold water
• con jabón = with soap
• de madera = made of wood

If you add an article, it sounds more specific:

• en el agua fría = in the cold water

That would suggest a particular cold water already known in the conversation.

Agua is feminine.

A common point of confusion is that singular agua often uses el instead of la:

• el agua
• el agua fría

This happens because agua starts with a stressed a sound, and la agua is awkward to pronounce. But the noun is still feminine.

You can see that it is feminine because:

• the adjective is feminine: fría, not frío
• in the plural it becomes las aguas

So in this sentence, even without an article, agua is still feminine.

Because agua is feminine, and adjectives must agree with the noun.

• agua fría
• not agua frío

Even when you see el agua, the noun itself is still feminine, so the adjective stays feminine too:

• el agua fría
• mucha agua
• agua limpia

It can mean either one, depending on context.

The Spanish present tense often covers both:

• a habitual action: I soak the clothes
• an action happening now: I am soaking the clothes

If you want to make the ongoing action extra clear, you can say:

• Estoy remojando la ropa en agua fría.

That is closer to I am soaking the clothes in cold water.

These verbs are related, but they are not the same.

• remojar = to soak
  You leave something in liquid for a while.
• mojar = to wet / to get wet
  Something becomes wet, but not necessarily soaked for a period of time.
• lavar = to wash
  You clean something.

Examples:

• Remojo los frijoles. = I soak the beans.
• La lluvia moja la ropa. = The rain wets the clothes.
• Lavo la ropa. = I wash the clothes.

So remojar is the right verb when the idea is soaking.

It is pronounced roughly like reh-MOH-ho.

A few pronunciation notes:

• the r is a soft Spanish r
• the j sounds like a strong English h, but farther back in the throat
• the stress falls on mo: re-MO-jo

So the stress is not on the last syllable.

Yes. That is very natural if you want to emphasize that the action is happening right now.

• Remojo la ropa en agua fría.
  = I soak the clothes / I’m soaking the clothes
• Estoy remojando la ropa en agua fría.
  = I am soaking the clothes right now

Both are correct; the second is more explicitly progressive.

Yes. A very common expression is:

• Pongo la ropa en remojo.

Literally, this is I put the clothes to soak or I put the clothes in soak, but in natural English it means I soak the clothes or I leave the clothes soaking.

So:

• Remojo la ropa en agua fría is correct and clear
• Pongo la ropa en remojo is also very natural in everyday Spanish

Yes. Since ropa is grammatically singular, anything that agrees with it is usually singular too.

For example:

• La ropa está mojada. = The clothes are wet.
• La ropa limpia = the clean clothes
• Mucha ropa = a lot of clothes

This is normal Spanish grammar: the meaning may be plural in English, but the noun is singular in Spanish.