It's often times better to start by modifying themes that already exist; you can learn quite a lot this way, and you'll definitely get to know how to build your own theme after a while. YMMV. No matter which way you choose you'll always need a lot of patience. Without patience you'll never really get to know how LS works. Even if it takes weeks or months, never give up. It's worth it in the end, and highly addictive.