Ispod tog drveta ljeti sjedimo u hladovini.

Because ispod requires the genitive case, so both the demonstrative and the noun have to change form.

• dictionary form: to drvo = that tree
• after ispod: tog drveta = under that tree

So the sentence uses:

• tog = genitive singular of taj/to
• drveta = genitive singular of drvo

Drveta is genitive singular.

The noun is:

• nominative singular: drvo
• genitive singular: drveta

This is a neuter noun, and neuter nouns in -o often form the genitive singular in -a.

Yes, ispod normally takes the genitive.

Examples:

• ispod stola = under the table
• ispod mosta = under the bridge
• ispod tog drveta = under that tree

This is different from pod, which can take different cases depending on meaning.

Both can relate to under/below, but they are not used in exactly the same way.

A simple way to think of it:

• ispod = below/underneath, often focusing on position beneath something
• pod = under, often the more basic preposition and used in some different case patterns

In a sentence like this, ispod tog drveta sounds very natural for under that tree.

Compare:

• sjedimo ispod drveta = we are sitting under the tree
• pas je pod stolom = the dog is under the table

You do not always choose them freely, so it is best to learn common patterns.

Ljeti is an adverb, meaning in summer or during the summer.

It refers to time, just like English in summer.

Examples:

• Ljeti je vruće. = It is hot in summer.
• Ljeti sjedimo u hladovini. = In summer we sit in the shade.

Even though it looks like a special form, in modern Croatian you can simply learn it as a fixed time adverb.

Sjedimo is the 1st person plural present tense of sjediti.

It can mean either:

• we sit
• we are sitting

Which English version fits depends on context.

Here it has a habitual/general feeling, especially because of ljeti, so English often uses:

• we sit
• we usually sit

The verb sjediti describes the state of being seated, not the action of sitting down.

This is a very important Croatian verb pair.

• sjediti = to be sitting, to sit
• sjesti = to sit down

So:

• sjedimo = we are sitting / we sit
• sjednemo or sjednuti / sjesti forms = we sit down

In this sentence, the idea is not the movement of taking a seat, but the state/location, so sjedimo is correct.

In Croatian, the subject pronoun is often omitted because the verb ending already shows the person.

• sjedim = I sit / I am sitting
• sjediš = you sit
• sjedimo = we sit

So sjedimo already means we sit.

You can add mi for emphasis:

• Mi sjedimo u hladovini. = We sit in the shade.

But in a normal sentence, it is usually unnecessary.

Hladovini is locative singular.

The preposition u can take different cases, but when it means in as a location, it takes the locative.

So:

• hladovina = shade
• u hladovini = in the shade

This is a standard pattern:

• u kući = in the house
• u školi = at school / in school
• u hladovini = in the shade

Yes, very often you can.

Both can mean in the shade, but there is a slight nuance:

• hlad = shade, coolness
• hladovina = a shady place, shade as an area

So:

• u hladu
• u hladovini

are both natural, and in many everyday contexts they are very close in meaning.

No, Croatian word order is fairly flexible.

Ispod tog drveta ljeti sjedimo u hladovini is natural, but other orders are also possible, depending on emphasis.

For example:

• Ljeti sjedimo ispod tog drveta u hladovini.
• U hladovini sjedimo ispod tog drveta ljeti.

The original sentence puts ispod tog drveta first, which helps set the scene. English usually has less flexibility than Croatian, so Croatian word order often reflects emphasis and information flow rather than strict grammar rules.

That is because to is the nominative singular form, but after ispod you need the genitive.

For the demonstrative taj, the relevant forms are:

• masculine nominative: taj
• feminine nominative: ta
• neuter nominative: to

But in the genitive singular, masculine and neuter use tog.

So:

• to drvo = that tree
• ispod tog drveta = under that tree

This is completely normal Croatian declension.