Abarim Publications' online Biblical Hebrew Dictionary
ב
The particle ב (be) basically means in, either in a spatial sense, or temporal (within a time frame), and even conditional, predicative and causal (in, as, because of).
It sometimes serves to indicate proximity (by, near), instrumentality (by means of) or even antagonism (against, upon). It's the first letter of the Bible; the "in" of "in the beginning."