Learn Danish: Alle skal gøre en indsats for miljøet. - Everyone has to make an effort for the environment.

In Danish, gøre is used for abstract actions and fixed expressions (like making a difference or making an effort), whereas lave is used for physically producing, creating, or preparing something concrete (like making food). Since an effort (en indsats) is abstract, gøre is the correct choice.

Could I use må instead of skal to mean "has to"?

Not here. Skal expresses a strong obligation, necessity, or expectation. Må usually expresses permission ("may" or "is allowed to"). If you said Alle må gøre en indsats, it would sound more like everyone is allowed to make an effort, rather than being required to do it.

The English translation says "everyone". Why use alle instead of enhver?

Alle (literally "all") is the standard, natural way to refer to "everyone" collectively in Danish. Enhver means "every single person" or "anyone" and places a heavy emphasis on the individual rather than the group. For a collective societal goal like helping the environment, alle is much more appropriate.

Why do we use the preposition for rather than til in this context?

You use for when an action is done to benefit, protect, or support something. That is exactly what making an effort for the environment implies. Til is generally used to indicate physical direction or the recipient of a direct, concrete transfer (like giving a letter to someone).