Learn Spanish (Spain): Marzo y abril son para descansar.

In Spanish, months of the year are not capitalized. They are always written in lowercase. Marzo is only capitalized here because it is the very first word of the sentence. Since abril is in the middle of the sentence, it stays lowercase.

The English translation says "resting". Why does the Spanish sentence use the dictionary form descansar (to rest)?

In English, we often use the "-ing" form after words like "for" (for resting). In Spanish, whenever a verb comes directly after a preposition like para, it must stay in its basic infinitive form, which is the form that ends in -ar, -er, or -ir. That is why we use descansar instead of an "-ing" equivalent.

Why do we use son instead of están for "are"?

We use son (a form of the verb ser) because we are describing the fundamental purpose or a permanent fact about these months. You use estar for temporary conditions or locations, but the purpose of March and April does not change here.

Why do we use para instead of por in this sentence?

The word para is used to express a purpose, goal, or intended use. Because we are talking about what March and April are used for (their purpose is resting), para is the right choice.