How do I troubleshoot my Audi A4 if it won't start?

I've tried turning the key in the ignition but the engine won't start. What steps should I take to diagnose and fix the problem?

First, check the battery to make sure it has enough charge. If the battery is the issue, jump-starting or replacing it may solve the problem.

If the battery seems to be working properly, try checking the starter and ignition system. A faulty starter or ignition switch could be preventing the engine from starting.

It's also important to check for any electrical issues, such as loose connections or a blown fuse, that could be causing the problem. Make sure all connections are secure and fuses are intact.