“Ou bien” is a set phrase which is practically synonymous with “ou” or “soit”: the whole phrase “ou bien” means “or” (or “either” when it’s in lead position). It is usually constructed like “soit”, i.e. it is present before the first alternative as well as between alternatives. The following are roughly equivalent and mean “[either] A or B”:

A ou B
A ou alors B   (usually used when A and B are very long phrases)
A ou bien B
ou bien A, ou bien B
soit A soit B

There is a nuance in that “soit” is more likely to be an exclusive or, and “ou bien” a little more likely to be exclusive than “ou”. However, all the formulations can either be exclusive or inclusive. In math, “ou” is always exclusive, but in everyday language, it’s often exclusive and “et/ou” can be used (mostly in writing) to indicate an inclusive or (and like “and/or” in English, not everyone likes it). “Ou bien” and “soit” are ambiguous even in math: they’re usually exclusive but can be inclusive.