Explanation
-아/어라 is the plain-speech (해라체) command ending, used to children, close friends, and in written commands or slogans. Use -아라 when the stem's last vowel is ㅏ or ㅗ (앉다 → 앉아라) and -어라 otherwise (먹다 → 먹어라); 하다 becomes 해라. It is blunt, so with anyone you address politely use -(으)세요, and note that reported commands take the separate -(으)라고, not -아/어라. 빨리 먹어라 — Eat quickly.