Learn Turkish: Lütfen bir harita alın.

The root al by itself is the informal, singular command. By adding -ın, you make it either plural for addressing multiple people, or formal and polite for addressing one person. Since the sentence starts with Lütfen (Please), this polite form fits perfectly.

How do I know whether to add -ın, -in, -un, or -ün for this formal command?

This suffix follows 4-way vowel harmony, which looks at the last vowel of the verb root. The root here is al-, and its vowel is a. In 4-way harmony, a or ı is always followed by ı, so the suffix becomes -ın.

Could I say Lütfen harita alın without the word bir?

Yes! Turkish often drops the equivalent of "a/an" when talking about general objects. However, using bir (a/one) here makes it slightly more specific, sounding like "Please take one map" rather than a general "Please take maps."

I've also seen words ending in -ınız. Could it be alınız here?