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When I was young, I do mix up some two words for each other which are faith and belief. I do think faith is the same thing as trust but as I continue to grow up and actually what made me understand better is the Bible which differentiate it well. So the word faith means having a great confidence it trust in someone. For one to have big confidence in someone there are some level which must have been met with the person. The Bible even made a definition that faith is what we hope for as evidence and those things which we are not privileged to see. So the other one which is belief is like putting your mindset in someone of doing something.
In reference to what 
It means that, by believing in the words of God, having the assurance that everything that is happening can be solved in one way or another, we can have faith and feel peace through it.
So having faith can create peace of mind
so the question goes thus: what should we believe in.
There are different things which people believe in based on their knowledge and where they grow up. So we can just belief in the things which we know it won't bring out good result. For me I believe in God because I can testify to his work in my life and that has given me an assurance of what to put my trust in or believe.
how can faith help us
Faith can help us to ease our mind off stress because that would have limit the trouble which one's mind would be getting
is faith related only to religion
I will say a big NO. because faith doesn't come along with religion only I have seen someone who doesn't attend church or either mosque and other form of religion but anytime he does something, he always say that he believe and have faith that those things will work out well and later on those things happen to work out so well and I know that one may not be in support of any religion yet have a big faith in things which he or she does.