Learn Swedish: Mannen promenerar ofta på torget. - The man often walks on the square.

In Swedish, open public spaces like squares (torg) usually take the preposition på (on) because you are on an open surface. You will also see this with streets (på gatan).

Could I use går instead of promenerar here?

Yes, but the meaning shifts slightly. promenerar specifically means to go for a walk or stroll for leisure. går is the general word for walking, going, or moving by foot.

Why does ofta come after the verb promenerar?

Swedish standard sentences follow the 'verb-second' rule, meaning the main verb is almost always in the second position. Since the subject (Mannen) is first, the verb (promenerar) is second, pushing the adverb ofta to the spot right after the verb.

Why does the word for 'the square' end in '-et' (torget)?

torg is an 'ett' word (ett torg). To make it definite and say 'the square', you add -et to the end. Nouns that use 'en' add -en instead.