yourself
The word you use to talk about you, yourself.
Yourself is the word you use when talking about you as a person, when you're both the one doing something and the one it's being done to. When you look at yourself in a mirror, you're seeing you. When you teach yourself to juggle, you're both the teacher and the student. When you remind yourself to bring your homework, you're giving yourself that reminder.
The word shows up in different ways. Sometimes it adds emphasis: “Did you build that treehouse yourself?” means “Did you do it without help?” Other times it completes an action that circles back: “Be proud of yourself” or “Don't blame yourself.”
People also use yourself to talk about who you really are, your true character. A coach might say “Just be yourself” before a big game, meaning don't try to act like someone else. When someone says “You're not acting like yourself today,” they notice you seem different from your usual personality.
The phrase by yourself means alone or without help: doing homework by yourself, sitting by yourself at lunch, or figuring out a puzzle by yourself. It can mean either solitude or independence, depending on the situation.