Questions & Answers about Останься здесь и не уходи!
Why is останься (stay) in the perfective aspect here?
When giving a direct, affirmative command for a specific, one-time action with a desired result, Russian typically uses the perfective aspect. You want the person to complete the action of staying right now.
The second command is не уходи (do not leave). Why does it switch to the imperfective aspect?
This is the golden rule of negative commands! When you tell someone not to do something (a prohibition), you almost always use the imperfective aspect, even if you only mean it for this one specific moment. That is why we use the imperfective уходи instead of the perfective уйди.
Why does останься end in -ся? I thought reflexive verbs sometimes end in -сь.
The base imperative form for "stay" is остань. Because it ends in a soft sign (ь), which acts like a consonant, we add the full -ся. You only use the shorter -сь after vowels (for example, in the past tense она осталась).
Could I use сюда instead of здесь for "here"?
No, you must use здесь. Сюда means "(to) here" and is strictly used with verbs of motion (like "Come here!"). Since staying in a place does not involve moving to a new location, you need the static location word здесь.