German Grammar Explained /

Conjunction: that

Ich glaube, dass er morgen kommt.
I think that he is coming tomorrow.
Since dass is a conjunction introducing a sub clause, you need to put the verb in the end and you need a comma to separate both clauses! German is very picky about separating clauses!
A difference to notice between German and English is that in English we avoid "that" whenever possible.
Ich habe Angst, dass wir den Flug verpassen.
I'm worried that we miss the flight.
You could leave dass out...
Ich habe Angst, wir verpassen den Flug.
I'm worried we miss the flight.
But this is just two main clauses (mind the verb) joined together by a comma. This type of elision is more common in English and it's used in German only in colloquial or spoken language.