To believe that (something) is right or desirable.(verb)
To have confidence in the ability or power of.(verb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "believe in" in a sentence
"The principal ones comprise between one and two millions and may be subdivided, or classified as follows: (1) Khylsti (Flagellants), who believe in severe penances, reject the Church, its sacraments, and usages."
"“On the other hand, they could very well believe in God,” Dilara said."
"Because he wants to believe in the myth of Amanda Jones and her colt legs, that inside the closed circle of the cool kids is a place for all of us."