There are a few meanings of the phrase "believe in ___". One meaning of "believe in ___" is to believe that something exists, or to believe that something is true. For example:
Do you believe in ghosts?
Not all people who believe in the Bible think that the story of Eden is literally true.
But another type of "believe in" is to believe that someone will be able to succeed. For example, parents tell their kids this to encourage them:
I believe in you.
A reader has asked how "believe in (someone)" is different than "trust (someone)". One difference is that when you "trust" someone, it means that you think that they'll:
- do the right thing
- not mess up
- not do something to hurt you (lying, stealing, cheating, etc.)
But when you "believe in" someone, you think that they'll accomplish something great:
I grew up never taking risks because I never felt like my parents believed in me.