Learn French: Vous pouvez protéger la nature si vous recyclez.

In French, you must use a definite article (le, la, les) when talking about general concepts or things as a whole. Because we are talking about nature in general, it translates to la nature.

Why is protéger in its infinitive (unconjugated) form?

When you have two verbs back-to-back, the second verb stays in the infinitive (the dictionary form). Here, the first verb pouvez (can/are able to) is conjugated, so protéger (to protect) stays in its unconjugated form.

How does the word si (if) affect the verbs in this sentence?

It doesn't change the tense here. When stating a general truth or fact, French uses the present tense for both parts of a si (if) sentence: vous pouvez (present) and si vous recyclez (present).

Is nature always feminine?

Yes, la nature is a feminine noun. A helpful tip for A2 learners: almost all French nouns ending in -ure (like la voiture, la culture, la chaussure) are feminine.