To lean on someone, means to depend on that person. For example, when you are sick and cannot get out of bed, you lean on your mother or partner to help you. They make you soup, bring you books to read, and listen to how you are feeling. They make you feel better physically and emotionally!
“I can always lean on my mom when I am having a hard time in school. “
“You know you can lean on me whenever you need help!”
“Brian is such a kind person. I can always lean on him when I am feeling sad. “