How does one get from a "root" like "bhel" to the Latin "fulgere" (for example)? This sort of thing mystifies me no end.

E.g., for the word "refulgent" I see:

From Latin refulgere (to radiate light, to reflect), from re- (back) + fulgere (to shine). Ultimately from the Indo-European root bhel- (to shine or burn), which is also the source of blaze, blank, blond, bleach, blanket, and flame. Earliest documented use: before 1500.