Besides the source crwth mentioned, you can also take a look at the following guides and courses:
Create Your Own Cryptocurrency Just Like Bitcoin or LitecoinHow to Get Started on Creating Your Own CryptocurrencyIt's great that you are interested in crypto and want to test your programming skills to try and develop something. But you should know that according to CoinMarketCap, there are currently over 9000 different coins and tokens. This number is even higher because many coins are not listed. The majority of these have no reason to exist or have any valid use cases.
Ask yourself what is your goal, and what problems does your digital asset solve?
Can the same be completed with bitcoin or one of the other assets that already exists?
Have fun learning and good luck!