أم and أو >> have the same meaning of OR .. feel free to use them both noting that أم is more used in classical or formal arabic (language of novels and articles) . ولا (wala) have different meaning in classical arabic .. it means NOR .. noting that it can be used in informal arabic (spoken one) by putting "shadda" "شدة" .. it is said "walla" ex: ؟ستذهب الي المدرسة ولّا البيت

اذا تريد ان تتحدث بالفصحى، او = ام لو حابب تتكلم عامية، او = ولا

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 ...