Learn Hardcore Czech: V čekárně sedí pět lidí. - Five people are sitting in the waiting room.

In this sentence it is followed by čekárně, which is in the locative case.
The preposition v normally takes the locative case when it means location (where something is):

v čekárně – in the waiting room
v Praze – in Prague
v autě – in the car

Why is it čekárně and not čekárna or čekárnu?

The noun’s basic (dictionary) form is čekárna – nominative singular (the form you’d look up).

Here, because of the preposition v with a static location (where?), you must use the locative singular:

nominative: čekárna – a waiting room
locative: čekárně – (in) the waiting room

So:

V čekárně sedí pět lidí. – Five people are sitting in the waiting room.

You would use čekárnu (accusative) mainly after verbs of motion into something:

Jdu do čekárny. – I am going into the waiting room.

Is čekárně singular or plural?

čekárně is singular, locative singular of čekárna.

The plural forms are:

nominative plural: čekárny – waiting rooms
locative plural: v čekárnách – in (the) waiting rooms

So:

V čekárně sedí pět lidí. – in the/a waiting room (one room)
V čekárnách sedí pět lidí. – in (the) waiting rooms (several rooms)

What exactly does čekárna mean? Is it only for doctors?

čekárna is a waiting room / waiting area in general, not just at a doctor’s office. It can be:

čekárna u lékaře – doctor’s waiting room
čekárna na nádraží – waiting room at a railway/bus station
letištní čekárna – airport waiting area

Context normally tells you what kind of waiting room it is.

Could you also say Pět lidí sedí v čekárně? Does the word order change the meaning?

Yes, Pět lidí sedí v čekárně is also correct.

Both mean the same basic thing:

V čekárně sedí pět lidí. – The place (waiting room) is more in focus: In the waiting room, (there) are five people sitting.
Pět lidí sedí v čekárně. – The number of people is more in focus: Five people are sitting in the waiting room.

Czech word order is relatively flexible; it is often used to highlight what is new or important in the sentence (topic–focus), not to mark grammar like in English.

Why is it pět lidí and not pět lidé?

In Czech, numbers 5 and higher are followed by the genitive plural of the noun.

The word lidé (people) has the genitive plural lidí. So:

nominative plural: lidé – people
genitive plural: lidí – (of) people

After pět you must use genitive plural, so:

pět lidí – five people (literally “five of people”), not pět lidé.

Other examples:

pět studentů – five students
pět aut – five cars
pět žen – five women

What is the singular form related to lidí? Why not just člověk?

The word lidé means people and is the plural of člověk (person). It’s irregular:

singular: člověk – person, human
nominative plural: lidé – people
genitive plural: lidí – of people (used after pět and other high numbers)

So:

jeden člověk – one person
dva / tři / čtyři lidé – two / three / four people (nominative plural)
pět lidí – five people (genitive plural)

How do the forms change with different numbers, for example 1, 2, 4, 5?

With člověk / lidé / lidí the patterns are:

1 person
- V čekárně sedí jeden člověk.
  (nominative singular člověk)
2, 3, 4 people
- V čekárně sedí dva lidé. – two people
- V čekárně sedí tři lidé. – three people
- V čekárně sedí čtyři lidé. – four people
  (nominative plural lidé)
5 and more people
- V čekárně sedí pět lidí. – five people
- V čekárně sedí deset lidí. – ten people
  (genitive plural lidí)

So the case of the noun changes depending on the numeral.

Why is sedí used here, and not something like jsou?

sedí is the 3rd person present of sedět – to sit / to be sitting.

In this sentence you describe what the people are doing, not just that they exist:

V čekárně sedí pět lidí. – Five people are sitting in the waiting room.

If you said:

V čekárně jsou (pět lidí).

this would be unnatural as a complete sentence. To express pure existence/location, you’d usually say:

V čekárně jsou lidé. – There are people in the waiting room.

But once you give the exact number pět, Czech prefers the pattern with the verb of activity (sedí, čekají, stojí, etc.).

In English we say There are five people…. Why is there no word for there at the start in Czech?

Czech doesn’t use a dummy word like English there to start existential sentences.

English:

There are five people sitting in the waiting room.

Czech expresses the same idea simply by putting the place first:

V čekárně sedí pět lidí. – In the waiting room sit(s) five people.

So the function of English there is often taken over by word order (place first, then verb, then subject). No special pronoun is needed.

Which person and number is sedí, and does it agree with pět lidí?

sedí is both:

3rd person singular (on/ona/to sedí)
3rd person plural (oni sedí)

The form is the same for singular and plural in this verb class.

With numbers 5 and higher, the phrase pět lidí behaves grammatically more like a neuter singular noun phrase, especially in the past tense:

present: V čekárně sedí pět lidí. – (form doesn’t show singular/plural)
past (standard): V čekárně sedělo pět lidí. – literally “sat it (neuter sg.) five people”

In everyday speech people sometimes also say:

V čekárně seděli pět lidí. – treating them as plural people, but this is more colloquial and some consider it less correct.

So in the present tense you don’t see the difference, because sedí looks the same for singular and plural.

Could I say ve čekárně instead of v čekárně?

No, in this case you must say v čekárně.

Czech sometimes uses ve instead of v before certain consonant clusters to make pronunciation easier (e.g. ve škole, ve vlaku, ve Vídni), but v čekárně is already easy to pronounce, so it stays v.

So the natural form is only:

V čekárně sedí pět lidí. ✅
Ve čekárně sedí pět lidí. ❌ (incorrect)