N5
な
Do not, Don't (Prohibitive)
「家の中で走るな！」とお母さんが言った。
My mother said, “Don't run in the house!”
Explanation
「な」 after the dictionary form of a verb is a prohibition, 'don't …': 「行くな」 (Don't go). It is the strongest kind of command. It is used for warnings in emergencies (fire, earthquake), for harsh orders from a boss to a subordinate or between men, and on signs: 「入るな」 (No entry), 「触るな」 (Do not touch). In everyday polite speech, 'please don't' is 「〜ないでください」.
Mixed up with
「な」 after the dictionary form is a prohibition: 「行くな」 (Don't go!).
「な」 after the ます-stem urges someone to do it (a spoken shortening of 「〜なさい」): 「行きな」 (Go on, go), 「食べな」 (Go on, eat). The two meanings are opposite, so make sure which form it follows.
The sentence-final 「な」 of feeling (「いい天気だな」) is yet another thing.