I find that these two words can be used to express to collect or gather. what is the difference between them? thank you in advance.
From Merriam-Webster's online definition:
Did You Know? Cumulate and its far more common relative "accumulate" both come from the Latin word cumulare, meaning "to heap up." "Cumulare," in turn, comes from cumulus, meaning "mass." ("Cumulus" functions as an English word in its own right as well. It can mean "heap" or "accumulation," or it can refer to a kind of dense puffy cloud with a flat base and rounded outlines.) "Cumulate" and "accumulate" overlap in meaning, but you're likely to find "cumulate" mostly in technical contexts. The word's related adjective, "cumulative," however, is used more widely.
Beyond that, it can be said that accumulate is used about 30 times more frequently than cumulate, according to Google's Ngram Viewer.
On the other hand, the adjective cumulative is far more common than accumulative (again, see Google's Ngram viewer), so that in ordinary speech, snow accumulates, but cumulative totals are measured.