Otkad sam kupio novo ravnalo, zadaća izgleda urednije.

Here otkad means since or ever since.

It introduces a time clause:

• Otkad sam kupio novo ravnalo... = Since I bought a new ruler...

A closely related form is otkako, which means the same thing.

Also, in a question, Otkad? can mean Since when? But in this sentence it is not a question; it is a conjunction introducing a subordinate clause.

Because sam is a clitic, and Croatian clitics normally go in the second position of their clause.

So:

• standalone clause: Kupio sam novo ravnalo.
• after otkad: Otkad sam kupio novo ravnalo...

The conjunction otkad takes the first position, so the clitic sam goes right after it.

Croatian often leaves subject pronouns out when they are already clear from the verb form.

Here sam kupio already tells you the subject is I:

• sam = first person singular auxiliary
• so ja is understood automatically

You could say Otkad sam ja kupio..., but that would add emphasis or contrast, something like Since I bought... rather than someone else.

In the Croatian past tense, the l-participle agrees with the subject in gender and number.

So:

• sam kupio = I bought (male speaker)
• sam kupila = I bought (female speaker)

As written, the sentence sounds like it is spoken by a man. If the speaker were a woman, it would be:

• Otkad sam kupila novo ravnalo, zadaća izgleda urednije.

Because kupiti is a perfective verb, and it fits a single completed action:

• kupio = bought / have bought, one finished purchase

That works well here because the sentence refers to one specific moment: buying the new ruler.

If you used kupovao, from the imperfective kupovati, it would suggest repeated buying, habitual action, or focus on the process, which does not match the meaning here.

Because ravnalo is a neuter singular noun, and the adjective has to agree with it.

So:

• novo = neuter singular form of nov
• ravnalo = neuter singular noun

Together:

• novo ravnalo = new ruler

Also, as the direct object of kupio, it is in the accusative, but for an inanimate neuter singular noun, the accusative looks the same as the nominative. So the form stays novo ravnalo.

Because Croatian has no articles.

English says:

• a new ruler
• the homework

Croatian simply says:

• novo ravnalo
• zadaća

Whether something is definite or indefinite is usually understood from context, word order, or the situation.

Zadaća can mean:

• homework
• assignment
• task

In a school context, it very naturally means homework.

In this sentence, it is singular, but that is normal. Like English homework, Croatian can use a singular noun to refer to the work as a whole.

The form urednije is the natural choice here after izgleda.

It means more neatly / neater, and Croatian often uses forms like:

• izgleda lijepo = looks nice
• izgleda bolje = looks better
• izgleda urednije = looks neater

So even though zadaća is feminine, the complement after izgleda is very often this kind of general descriptive form rather than an agreeing feminine adjective.

A form like urednija is not impossible in all contexts, but izgleda urednije is the more idiomatic way to say that the homework now has a neater appearance.

Because Croatian, like English, can use a comparative without stating the comparison explicitly when the comparison is obvious from context.

Here the meaning is:

• the homework looks neater now
• implicitly: than before I bought the new ruler

So the comparison is understood from otkad sam kupio novo ravnalo.

Because the sentence begins with a subordinate time clause, and Croatian normally separates that clause from the main clause with a comma.

So the structure is:

• Otkad sam kupio novo ravnalo, = subordinate clause
• zadaća izgleda urednije. = main clause

This is standard punctuation in Croatian.