It's time to start setting limits, or teaching your child what he should not do, when he begins to crawl. His curiosity about the world is combined with inexperience about safety and the inability to control impulses. It will take a lot of repetition before your baby understands what "no" means. At this stage, your baby needs your consistent and caring guidance to keep him safe while he explores his environment.
Create a safe play space so that your baby can move through the house without constantly being told "don't touch" and "don't do that." For example, cover electrical outlets and remove breakable objects from reach.
During toddlerhood, your child is ready for additional guidance about how to treat other people and objects. Rules like "no hurting others" and "you can touch the plant, but only very gently" can be helpful.
This is also the stage to begin teaching your child what kinds of behaviours you expect from her. For example, tell her that "when we want something, we say 'please.'"
Remember that it takes a long time for children to develop the ability to remember the limits and expectations without being reminded. And, once they do remember, sometimes they'll want to exercise their independence by deciding to break the rules. When this happens, patiently remind your child of the rule.