The command can be used two ways in Spanish; 1. Imperative 2. Subjunctive 1. Ponte en la silla. 2. Póngase en la silla / qué se ponga en la silla / qué te pongas en la silla. *keep in mind that commands that begin with "qué" should only be used in very familiar situations and never used with complete strangers because it can sound too direct. It is very typical when a parent scolds a child.*

Because you are commanding someone to do something, and it's a direct communication between you and a 2nd person (even if that person is you, you play 2 roles), one has the power to order and the other the subordination to follow, but not always is the case. Naturally, it can only be conjugated toward the 2nd person, singular or plural, no matter what. The mood is called "imperativo". I hope you have a nice day!

When I use English to talk to myself, I am both the speaker and the listener at the same time. When I address myself as the listener, I address myself as "you", and not as "I". Likewise, when I use Spanish to talk to myself and I address myself as the listener, I address myself using 2nd-person singular pronouns. It's the same when I give myself a command: I use 2nd person imperative forms.