Setting Boundaries

Boundaries show where one thing ends and another begins. Boundaries in a relationship are kind of like this;They help each person figure out where one person ends and the other begins. In short, boundaries help you define what you are comfortable with and how you would like to be treated by others.
Boundaries that are healthy. We all know we need them to achieve work/life balance, deal with toxic people, and have rewarding relationships with partners, friends, and family. But what exactly do "healthy boundaries" entail, and how can we express our needs, say "no," and be assertive without offending others?