As verbs, what are the differences and relation between certify and certificate?
For example, in human resources, why is it effort certify not effort certificate?
"Certify" is a verb, "certificate" is a noun. You would issue a "certificate of effort" if you were to "certify effort".
Using "certificate" (long a there) as verb is an error, I would say. The listener will understand what you're saying, but it falls under the same heading as "orientate" (as opposed the shorter identical verb "orient"), in my estimation.
Certify has a bit more variability to it in my opinion. Merriam Webster offers "to inform with certainty". In this sense it may be used to simply mean confirm, assure, verify, etc. (A friend recently asked me, "Could you certify that he is a reliable man?") In other cases it could also mean allow, especially in computer contexts.
Meanwhile, certificate would almost always mean to grant a certificate, or at the least to decree something in an outright official manner.
As for me, I would never use the latter. It sounds a bit too much like business jargon to be taken seriously in my mind.