The concept is actually quite simple. Say, when you're using something that is loud and heavy, if you put your hands on it, you could probably feel it vibrating.

Everything in the universe has a subtle vibration - some things more pronounced than others - including you and your thoughts. Every vibration has a frequency - faster or slower. The slower the vibration, the more heavy and dense it gets. The faster (or higher, as some call it) the vibration, the lighter and less dense it gets.

Happiness and positive thoughts are often of a high vibration. So, when people tell you to "raise your vibration" they are literally telling you to "lighten up", to become lighter and think more positive thoughts.

Does this help?