Observe the market, more specifically few selected stocks for few days. Consider that you have bought them with paper money (not real money) now keep an eye on to see how your money is progressing. This will give you a good feel of how prices fluctuate with you having to invest your actual money. Practice makes it perfect!if you wish to have confidence in yourself, you must earn it for yourself.
The only way you can know your abilities is by putting them to work. Real confidence comes from your own experience of doing.
Understanding the stock market can never be mastered. It will require the stock market investor or day trader to put to practice what they have learned and repeat the process until they master the topic.
Good luck and safe trading!