Většina sousedů je v komunitní zahradě.

Because většina means the majority / most of, and after this kind of word Czech normally uses the genitive.

• většina = nominative singular
• sousedů = genitive plural of soused

So většina sousedů literally works like the majority of the neighbors.

Using sousedi here would be ungrammatical.

The grammatical subject is většina, which is a singular noun. Because of that, the verb agrees with většina, not with sousedů.

So:

• Většina sousedů je ... = standard
• literally: The majority of the neighbors is ...

Even though English usually says most of the neighbors are, Czech commonly keeps the verb singular with většina.

For a learner, the best answer is: use je.

In standard Czech, je is the normal and safest choice because většina is singular. You may occasionally hear plural agreement in informal speech when people focus on the actual group of neighbors, but je is the form you should learn and use.

After v meaning in, Czech usually uses the locative case.

Here:

• zahrada → v zahradě
• komunitní zahrada → v komunitní zahradě

So komunitní zahradě is locative singular.

Because adjectives have to agree with the noun they describe.

The noun zahrada is:

• feminine
• singular
• here in the locative

So the adjective komunitní must match it:

• komunitní zahrada = nominative
• v komunitní zahradě = locative

The noun changes to zahradě, and the adjective stays in the matching feminine singular locative form komunitní.

Mostly in.

V komunitní zahradě literally means in the community garden. In natural English, depending on context, you might also translate it as at the community garden, but the Czech preposition here is the normal one for being inside or within that place.

Yes. Czech word order is fairly flexible, and changing it usually changes focus rather than basic meaning.

For example:

• Většina sousedů je v komunitní zahradě.
  Neutral statement.

• V komunitní zahradě je většina sousedů.
  Puts more emphasis on where they are.

The original sentence is a natural, neutral order.

Because Czech does not have articles like the or a/an.

So:

• většina sousedů can mean the majority of the neighbors
• v komunitní zahradě can mean in the community garden

Czech relies on context instead of articles.

It is a noun, not just a simple adverb like English most.

It means:

• majority
• most of

That is why it behaves like a singular noun and can govern the genitive:

• většina lidí = most people
• většina studentů = most students
• většina sousedů = most of the neighbors

A rough pronunciation guide is:

VYET-shi-na SOU-seh-doo yeh f komunit-nee ZAHH-ra-dyeh

A few helpful notes:

• ě often sounds like ye after certain consonants, so většina begins roughly vyet-
• š sounds like sh
• ou sounds like the oa in boat
• ů is a long oo
• v is often pronounced more like f before a voiceless consonant, so v komunitní may sound a bit like f komunitní

Yes. Czech still normally agrees with většina as a singular noun.

For example:

• Většina sousedů byla v komunitní zahradě. = Most of the neighbors were in the community garden.

Notice byla is singular, not plural, because it agrees with většina.

Yes, very often. The pattern is:

většina + genitive plural noun

Examples:

• Většina studentů je ve škole.
• Většina lidí je doma.
• Většina dětí je venku.

So Většina sousedů je v komunitní zahradě is a very useful model sentence.