Learn Swedish: Du ska inte peka med fingret. - You should not point with your finger.

In Swedish, when it is obvious whose body part is involved, you use the definite form (fingret) instead of a possessive pronoun (ditt). Since you are the one pointing, it is automatically understood that it is your own finger.

Doesn't ska usually mean "will"? Why is it translated as "should" here?

While ska often marks the future tense, it is also used to express a strong rule, obligation, or reprimand. In this context, Du ska inte... acts as a firm instruction, similar to "You are not to..." or "You must not..." in English.

Why do we need the preposition med (with) here?

In English you might just say "point your finger," but in Swedish you point with your finger (peka med fingret). If you wanted to add what you are pointing at, you would use the preposition på, as in peka på något.

Why does inte come before peka?

This is standard Swedish word order for a main clause. The negative word inte usually comes immediately after the first verb. Because the first verb is the helping verb ska, inte slips in right after it, before the main verb peka.