Po večeři si moje sestra objedná kávu a sladký dezert.

Because po meaning after takes the locative case in Czech.

• dictionary form: večeře = dinner
• after po, it changes to večeři

So:

• po večeři = after dinner

This is a very common pattern:

• po obědě = after lunch
• po škole = after school
• po práci = after work

With večeře, the locative singular form is večeři.

Here si is a short form of the reflexive pronoun in the dative. In this sentence, it shows that the sister is ordering something for herself.

So:

• objednat = to order
• objednat si = to order for oneself

That is why objedná si kávu means she will order herself a coffee or more naturally in English, simply she will order a coffee.

In many cases, English does not translate si directly, but Czech often uses it.

Objedná is the present form of a perfective verb, and in Czech, that usually has future meaning.

So:

• objednat = perfective, completed action
• objedná = he/she will order

If you wanted a present or habitual meaning, you would usually use the imperfective verb:

• objednává = he/she is ordering / he/she orders regularly

So this sentence suggests a single completed future action: after dinner, she will order coffee and a sweet dessert.

Because kávu is the accusative singular form of káva.

It is the direct object of the verb objedná si:

• What will she order? → kávu

For many feminine nouns ending in -a, the accusative singular changes -a to -u:

• káva → kávu
• voda → vodu
• sestra → sestru

Because dezert is also a direct object here, so it is in the accusative singular.

However, dezert is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular is often the same as the nominative singular.

So:

• nominative: sladký dezert
• accusative: sladký dezert

That is why nothing changes on the surface.

By contrast:

• káva → kávu changes clearly
• dezert → dezert stays the same

The adjective sladký has to agree with dezert in:

• gender
• number
• case

Since dezert is:

• masculine inanimate
• singular
• accusative

the adjective takes the matching form sladký.

Because masculine inanimate accusative singular looks the same as nominative singular, the adjective also stays in the basic-looking form.

Moje sestra means my sister.

• moje = my
• sestra = sister

Czech often includes possessives when they are useful or natural, just like English. You could say simply sestra in some contexts, but moje sestra makes it explicit whose sister is meant.

Also, moje agrees with sestra:

• feminine
• singular
• nominative

Because it is the subject of the sentence, so it is in the nominative case.

The person doing the action is:

• moje sestra = my sister

That is why sestra stays in its basic dictionary form here.

The sentence is:

Po večeři si moje sestra objedná kávu a sladký dezert.

A natural breakdown is:

• Po večeři = time expression
• si = reflexive/dative pronoun
• moje sestra = subject
• objedná = verb
• kávu a sladký dezert = objects

Czech word order is more flexible than English, but this order sounds natural and neutral. The first part, Po večeři, sets the time: after dinner.

Normally, no. Because objedná is from a perfective verb, it usually points to a future single action:

• After dinner, my sister will order coffee and a sweet dessert.

If you want a habitual or repeated action, Czech would more naturally use the imperfective verb:

• Po večeři si moje sestra objednává kávu a sladký dezert.

So the choice of verb aspect matters a lot.

No. Objednat si can be used in several contexts, for example:

• ordering food or drinks
• ordering goods
• booking or requesting something for oneself

But in this sentence, because the objects are kávu a sladký dezert, the restaurant/café meaning is the natural one.

Czech does not have articles like English the and a/an.

So:

• kávu can mean coffee, a coffee, or sometimes the coffee
• sladký dezert can mean a sweet dessert or the sweet dessert

The exact meaning depends on context. English must choose an article, but Czech usually does not mark that distinction directly.

In Czech, it is simply po večeři, without an article. Depending on context, English may translate it as:

• after dinner
• after the dinner

In most everyday situations, after dinner is the most natural English translation. Czech does not force the article distinction the way English does.

Yes, you may sometimes encounter both večeři and večeře in certain patterns or styles, but po večeři is the normal and standard form here.

For a learner, the important thing is:

• learn the expression po večeři as a fixed, common phrase meaning after dinner.

In neutral speech, the main stress of each word stays on the first syllable, which is standard in Czech:

• PO večeři si MOje SEstra obJEDná KÁvu a SLADký DEzert

But in terms of sentence focus, the last part often carries the main informational weight:

• kávu a sladký dezert

So if said neutrally, the ending may sound slightly more prominent because it gives the new information.