The imperative mood is used to give commands. Whenever you use “ты” (such as with a friend or family member), you should replace the verb ending with -й / -и. And whenever you use “вы” (such as with a group of people or a stranger), you should replace the verb ending with -йте / -ите. Some imperatives end with -ь or -ьте. There is a rule for that. But it is quite complicated. At this stage we suggest just memorizing the most often used imperatives.