Learn Dutch: Er wandelen veel opa's in het park. - Many grandpas are walking in the park.

In Dutch, nouns ending in a single open vowel like a, i, o, u, or y get an apostrophe-s ('s) for the plural. If you just added an s to make opas, the rules of Dutch pronunciation would make the a sound short. The apostrophe protects the long vowel sound in opa.

Why does the sentence start with Er instead of just saying Veel opa's wandelen in het park?

Er is often used as a placeholder to introduce new, non-specific information, similar to "There are" in English. While you could technically say Veel opa's wandelen..., Dutch speakers heavily prefer using Er when the subject is indefinite (like "many grandpas" or "a dog").

If veel opa's is the subject, why does the verb wandelen come before it?

This is because of the Dutch "verb second" rule. In a normal main sentence, the conjugated verb must be the second piece of information. Here, the word Er takes the first spot, so the verb wandelen takes the second spot. The actual subject, veel opa's, simply follows it.

Why is it veel instead of vele here?