believe in something           
phrasal verb with believe verb [ T ] uk/bɪˈliːv/ us/bɪˈliːv/
B1 确信;信奉
to be certain that something exists
  Do you believe in ghosts? 你相信有鬼吗? 
 B2 对…有信心;认为…有效(或正确)
to be confident that something is effective and right
  They don't believe in living together before marriage. 他们认为婚前同居不好。 
 He believes in saying what he thinks. 他认为说出自己的想法是对的。 
 - More examples
 - Some people believe in life after death.
 - She strongly believes in the curative powers of the local mineral water.
 - Do you believe in an all-powerful god ?
 - Did you believe in fairies when you were little?
 - The tragedy made her question everything she believed in.