Learn Dutch: Overal zien we dieren. - Everywhere we see animals.

In Dutch, the main verb almost always takes the second position in a sentence. Because this sentence starts with the word Overal (Everywhere), the verb zien (see) must come next. This pushes the subject we into the third position. This swapping of the subject and verb is called inversion.

Could I use wij instead of we in this sentence?

Yes, but we is usually more natural here. Both mean "we", but we is the unstressed, everyday version. You would only use wij if you wanted to strongly emphasize that we are seeing animals, as opposed to someone else seeing them.

How is the plural dieren formed?

The singular word for animal is dier. In Dutch, most nouns become plural by adding -en or -s to the end. Adding -en to dier gives us the plural dieren (animals).

Why isn't there a word like de (the) before dieren?

Just like in English, you don't use an article when talking about unspecified plural things in general. You just say dieren (animals). If you were talking about specific animals you had already mentioned, you would say de dieren (the animals).