In general means أو however it can be أم too in some cases .. for ex : هل اللغة العربية صعبة أم لا = Is the Arabic language difficult or not ... ولا is different means ( nor ) in English and it uses for two negatives like, I'm neither a liberal nor a conservative = أنا لستُ ليبرالياً ولا محافظاً
I hope that's help ...