This is a good question. You will find many people wanting to sell your life purpose to you - in other words, if you buy and follow their teachings you will definitely discover your life purpose, and until you have spent that money you will be drifting.
Nothing could be further from the truth.
Some people have a life purpose that brings them fame, for example someone like Nelson Mandela who was born to teach us all about peace and tolerance and forgiveness.
Other people have a life purpose that they visibly live every day, for example an inspiring teacher or a nurse who is well-known in her community for a caring touch.
All people have a life purpose, which is to make a success of what they do every single day.
So how do you discover your life purpose? Ask your self at the end of every day what you have done that has given you satisfaction or a sense of achievement. Write your answer down.
You will very quickly discover what makes your life worth living (for yourself, not for other people), and once you have that awareness, focus on getting more of that good stuff done every day.
Every insight that you gain is also a step further down the path of spiritual growth. Sometimes the insight is that you love something, other times the insight is that something or someone is not good for you. Spiritual growth is that awareness of what you think, say and do every day, and how it impacts on your sense of peace and on the people around you.
If you are interested in a more focused spiritual growth path, I would suggest that you visit a bookshop with a mind, body spirit section and look through the books there. Don't worry about finding the ‘right’ book. Rather find any book that looks interesting to you, and read it. If you don't enjoy reading, look for interesting topics on YouTube and watch the videos.
Whatever you do, trust your inner voice. Do not believe anything unless you feel on all levels that there is a truth in it that resonates with you.