- Why did everyone start to hate the Russians if the U.S. did the same thing in Afghanistan, Iraq?
- What needs to be corrected in the management of Russia first?
- Why did Blaise Pascal become a religious man at the end of his life?
- How do I know if a guy likes you?
- When they say "one generation", how many do they mean?
Make no mistake that philosophers do nothing but think about the meaning of life. They care about a lot of completely different topics and tasks. Even if they are directly concerned with this particular subject, you should not think that you will understand what they have written outside the context of their philosophical system, and even more so you will learn something to solve your problems. You'd better start with something popular. For example, Leo Tolstoy's “Confessions” is very good. Or, for example, the Bible book “Ecclesiastes”. There are also ancient authors like those mentioned in another answer by Epicurus and Seneca [About the shortness of life, About the blissful life, etc.], but already with them you will be hard.
Certainly noteworthy are Aristotle, Plato, Epicurus and his school, as well as the Stoics, especially Seneca. I also recommend reading Sartre and Marx. And, of course, you can not do without religious philosophers of various faiths. After that, consider that you know the basic answers to the question about the meaning of life. Other – varieties or unpopular concepts.
I advise you to start not with books and philosophical teachings, but with something more understandable, because it is difficult to perceive philosophy in isolation from the life of a philosopher and other ideas.
I recommend to start with a series of films from the BBC – “geniuses of the ancient world” and “geniuses of the modern world”. Three movies each. The first three are about Socrates, Buddha, and Confucius, and the second three are about Freud, Marx, and Nietzsche.
The question of the meaning of life there, of course, is not the main one, but it is also raised. Plus it is very useful for general development and introduction to philosophy.