Ik weet dat jij thuis bent.
English: I know that you are at home.
In Dutch, 'bijzinnen met dat' are subordinate clauses that start with 'dat'. These clauses give extra information, often about what someone thinks, says, or feels.
Use this structure when you want to report what someone says, thinks, knows, or believes. It is common after verbs like 'zeggen', 'denken', 'weten', and 'vinden'.
Ik weet dat jij thuis bent.
English: I know that you are at home.
Hij zegt dat hij morgen komt.
English: He says that he is coming tomorrow.
We hopen dat het mooi weer wordt.
English: We hope that the weather will be nice.
Zij denkt dat het te laat is.
English: She thinks that it is too late.