Note! Many people and also a lot of Germans mix the conjunction dass with the relative pronoun das (3rd person singular neutral).

Have a look at these phrases.

a) Er sagt, dass er es macht. = He says that he does it.   b) Das Haus, das du da drüben siehst, gehört mir. = The house that you see over there is mine.

In phrase a) dass is a conjunction combining two clauses. The conjunction is written with ss. The phrase b) das is a relative pronoun that refers to the neutral word das Haus.

examples Er weiß, dass er das nicht darf. = He knows that he must not do this. Es ist mir egal, dass er nicht kommt. = I don't care that he doesn't come. Er langweilte sich derart, dass er ging. = He was bored that much that he left.