Penser que, croire que = To think that, to believe that

Look at these sentences:

ATTENTION 
When using verbs of opinions such as penser (to think) and croire (to believe) to say 'I believe that / I think that' in French, you always need to put que ('that') after them, whereas in English you can sometimes omit it.

For example: In French, you can NEVER say ''Vous pensez elle chante bien.'' or ''Elle croit les anges existent.''

See also the more advanced Using 'trouver' to express 'to find' and opinions  and Using Le Subjonctif after penser, trouver. savoir, croire, prétendre + que in the negative