When we are very happy or unhappy there are repetitive thoughts of happiness or unhappiness respectively. It is like we identify ourselves with the thoughts or we become the thoughts forgetting about anything else in those moments. Meditation means witnessing our body-mind. It is like watching our mind. This is possible by dissolving thoughts. There are different ways of reaching meditative state. A common way is to engage mind in one single act initially so that it does not form a chain of thoughts. This single act could be observing the sensation of breath or saying AUM mentally/orally or something else. Whenever mind jumps it needs to be brought back to this single act. Eventually, this act itself should go away and nothing else should be left except stillness. This is meditative state. It happens naturally and cannot be forced.