*I am not a teacher, these are just my own thoughts*
Are 'credence' , 'credit' and 'belief' the same?
Not exactly, you wouldn't replace one with the others in a sentence.
Belief is used in matters of faith or religion or whenever you may not have facts to support a conclusion or when you trust in something but don't know it to be true. I believe my husband is at work, but I don't know that for a fact.
Credence is not commonly used. I might say "This report gives credence to the idea of..." meaning that the report makes the idea believable, more trustworthy. Your "credentials" give "credence" to you, meaning that I will believe that I can trust you in some way.
In the same way that credence and credentials go together I would say that "credit" and "credible" are related. My dictionary says "credit: Belief or confidence in the truth of st: trust. The quality of being trustworthy or credible." "credible: capable of being believed; plausible. Worthy of confidence; reliable."
If I give you credit and let you borrow money, I believe that you will pay the money back. I have confidence that you are trustworthy and reliable. I might believe all this because you have good credentials. If someone asked why I gave you money I would answer, "Because I believe in him."
So all of these words are related to the same ideas but are used in very different ways.