Klamerica je na polici, ali spajalice su u ladici.

They are both present-tense forms of biti (to be), but they agree with number:

• je = is for singular
• su = are for plural

So:

• Klamerica je = The stapler is
• Spajalice su = The staples/paper clips are

Croatian verbs must match singular vs. plural just like English.

Because after na and u when they describe a fixed location, Croatian uses the locative case.

The dictionary forms are:

• polica = shelf
• ladica = drawer

But in this sentence they become:

• na polici = on the shelf
• u ladici = in the drawer

So the -a ending changes to -i in the singular locative for these feminine nouns.

Because Croatian uses different prepositions depending on the kind of location:

• na = on, at
• u = in, inside

A shelf is treated as a surface or place on which something is located, so you say na polici.

A drawer is treated as an enclosed space inside which something is located, so you say u ladici.

This works much like English:

• on the shelf
• in the drawer

Spajalice is the plural form. The singular is spajalica.

So:

• spajalica = one staple/paper clip
• spajalice = staples/paper clips

This is a very common feminine noun pattern:

• singular -a
• plural -e

For example:

• ladica → ladice
• spajalica → spajalice

Yes, all the main nouns in this sentence are feminine:

• klamerica
• polica
• spajalica
• ladica

A very common clue in Croatian is that nouns ending in -a are often feminine. That is not a perfect rule for every noun in the language, but it works for all of these words.

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

So a noun like klamerica can mean:

• a stapler
• the stapler

The exact meaning depends on context. The same is true for polici, ladici, and spajalice.

Ali means but.

It connects two contrasting ideas:

• Klamerica je na polici
• ali
• spajalice su u ladici

So it works just like English but in this sentence.

Because je and su are short unstressed forms, often called clitics, and in Croatian they usually appear in the second position of the clause.

So in a simple clause like this:

• Klamerica je na polici
• Spajalice su u ladici

the noun comes first, and the clitic verb form comes right after it.

You can also move other parts around, and the clitic still tends to stay near the beginning:

• Na polici je klamerica.
• U ladici su spajalice.

That is a very typical Croatian pattern.

Yes, often you can. Croatian word order is more flexible than English.

For example, these are also natural:

• Na polici je klamerica, ali u ladici su spajalice.
• Klamerica je na polici, ali u ladici su spajalice.

The basic meaning stays the same, but the focus changes a little:

• starting with Klamerica focuses more on the object
• starting with Na polici focuses more on the location

Then Croatian normally uses the accusative, not the locative.

Compare:

Location

• na polici = on the shelf
• u ladici = in the drawer

Movement toward a place

• na policu = onto the shelf
• u ladicu = into the drawer

For example:

• Stavljam klamericu na policu. = I am putting the stapler onto the shelf.
• Stavljam spajalice u ladicu. = I am putting the staples/paper clips into the drawer.

So:

• where something is → locative
• where something is going → accusative

In Croatian, c is pronounced ts, like the end of English cats.

So:

• polici sounds roughly like po-lee-tsee
• ladici sounds roughly like la-dee-tsee
• spajalice sounds roughly like spa-ya-lee-tse

Important: Croatian c is consistently ts. It is not pronounced like English k or s on its own.

Yes, in standard Croatian you normally keep the present-tense form of to be in this kind of sentence.

So you say:

• Klamerica je na polici.
• Spajalice su u ladici.

You would not normally drop je or su here. Unlike some other Slavic languages, Croatian keeps the present-tense copula in ordinary sentences of this type.