Umím plavat.

Umím is the 1st person singular form of the verb umět, which means to know how to, to be able to, or to have a skill.

So:

• umět = to know how to / can (in the sense of having learned ability)
• umím = I know how to / I can

In Umím plavat, umím means I know how to swim or I can swim.

After umět, Czech normally uses the infinitive of another verb.

So the structure is:

• umím + infinitive
• umím plavat = I know how to swim

Other examples:

• Umím vařit. = I can cook.
• Umím číst česky. = I can read Czech.

This is similar to English can swim, except Czech uses a full verb meaning know how to.

Czech often omits subject pronouns when they are clear from the verb ending.

The ending -ím in umím already tells you the subject is I.

So:

• Umím plavat. = I can swim.
• Já umím plavat. = I can swim.

Both are correct, but já is usually added only for emphasis, contrast, or clarity.

For example:

• Já umím plavat, ale on ne. = I can swim, but he can’t.

A simple approximate pronunciation is:

oo-MEEM PLAH-vaht

A few details:

• u = like oo in boot
• í = a long ee sound
• plavat has stress on the first syllable: PLA-vat
• Czech stress is usually on the first syllable of each word

So:

• Umím → OO-meem
• plavat → PLA-vat

This is a very common question.

• umím = I know how to, I have the skill
• můžu = I may / I am able to / I can in the sense of possibility, permission, or circumstances

So:

• Umím plavat. = I know how to swim.
  (I have the skill.)
• Můžu plavat. = I can swim.
  (I’m allowed to, or it’s possible right now.)

Examples:

• Umím řídit. = I know how to drive.
• Dnes nemůžu řídit. = I can’t drive today.

So in your sentence, umím is about ability learned as a skill, not permission.

Plavat is an imperfective verb.

That makes sense because swimming is an ongoing activity, and after umět, Czech commonly uses the basic infinitive of the activity or skill.

In this sentence, you do not need to worry much about aspect. The important thing is that:

• umět + infinitive expresses a general ability
• plavat is the normal verb for to swim

So Umím plavat means you have the ability to perform that activity in general.

Yes, Czech word order is flexible, but Umím plavat is the most neutral and natural order.

Possible variants include:

• Umím plavat. = neutral
• Plavat umím. = As for swimming, I can do that / Swimming, I can do.
• Já umím plavat. = I can swim. (with emphasis on I)

Changing the order often changes emphasis, not the basic meaning.

You make it negative by adding ne- to the verb:

• Umím plavat. = I can swim.
• Neumím plavat. = I can’t swim / I don’t know how to swim.

This is very common in Czech: negation is often built directly into the verb.

The simplest way is to keep the same words and use question intonation:

• Umíš plavat? = Can you swim?

Here the verb changes because the subject changes:

• umím = I can
• umíš = you can

You can also add pronouns if needed:

• Ty umíš plavat? = Can you swim?

But the pronoun is often unnecessary.

It can be used with both.

With actions:

• Umím plavat. = I can swim.
• Umím tančit. = I can dance.

With knowledge/skills such as languages or school subjects:

• Umím česky. = I know Czech.
• Umím matematiku. = I know math.

So umět is broadly about knowing something or knowing how to do something.

Here is the present tense of umět:

• (já) umím = I can / know how to
• (ty) umíš = you can
• (on/ona/ono) umí = he/she/it can
• (my) umíme = we can
• (vy) umíte = you can
• (oni/ony/ona) umějí / umí = they can

So your sentence uses the já form:

• Umím plavat.

Yes. The ending -ím marks 1st person singular present tense for this verb.

That ending tells you the speaker is I, which is why Czech does not need to say já unless it wants emphasis.

So even without a pronoun:

• umím already means I can / I know how

This is one of the key features of Czech verbs: they often show the subject through their endings.