The most important question is which questions matter. Time spent on questions that don't matter is wasted. And since most questions don't matter, the correct answer to most questions is "I don't know and I don't care".
The second most important question is how one should live one's life. Religions help with this question.
Asking which religion is true is a bad question. Religions can't be proven true. So one should choose one's religion based on which religion one thinks can best guide one in living life. Once one chooses, one should accept the assumptions of the religion. This is often called "faith". The Old Testament religion, Christianity, and Islam are all reasonable options.