Questions & Answers about Pjevaju i šetaju zajedno.
Where is the word for "they" in this sentence?
Croatian often drops the subject pronoun (like oni for "they") because the verb ending already tells us who is doing the action. The -ju ending on both pjevaju and šetaju clearly shows that "they" are the ones singing and walking.
How do we get pjevaju and šetaju from their dictionary forms?
The dictionary forms (infinitives) are pjevati (to sing) and šetati (to walk). For regular -ati verbs, you find the base by dropping the -ti, leaving pjeva- and šeta-. Then, for the "they" form in the present tense, you add the ending -ju, giving you pjevaju and šetaju.
Is it wrong to say Oni pjevaju i šetaju zajedno?
It is completely correct grammatically, but native speakers usually only add the pronoun oni if they want to emphasize exactly who is singing and walking. Otherwise, it sounds more natural to leave out the pronoun.
What role does i play here?
The word i simply means "and". It is a very common conjunction used to connect two verbs or ideas, just like in English. Here it connects pjevaju and šetaju.