Learn Hardcore Russian: Я ухаживаю за собакой.

In this sentence, ухаживать means "to take care of" or "to look after." Although the verb sometimes carries a romantic connotation (as in "to court" someone), here—paired with за and an animal—it clearly means providing regular care.

Why is the preposition за used in this construction, and what case does собакой represent?

The preposition за is used with ухаживать to indicate that the care or attention is directed toward someone or something. In this structure, the noun following за must be in the instrumental case. Thus, собакой is the instrumental form of собака, showing that it is the object being cared for.

How is the verb in "Я ухаживаю за собакой" conjugated for the first person singular, and what is its infinitive?

The infinitive is ухаживать. For the first person singular in the present tense, it is conjugated as ухаживаю. This form indicates that the speaker is currently or habitually taking care of the dog.

Why is собакой used instead of the nominative собака?

Собакой is used because the verb phrase ухаживать за requires its object to be in the instrumental case. Instead of the nominative собака, the word shifts to собакой to maintain the correct grammatical structure for expressing care or attention in Russian.