"The man knows us."
Translation:De man kent ons.
"Weten" and "kennen" are used in different ways, and most of the time they are not interchangeable.
Kennen is transitive, it always needs a direct object. More specifically, it means "to be acquainted with" or "to be familiar with". It is used when you know an object or a person.
- Ik ken dat boek - I know that book (or: I am familiar with that book)
- Ik ken jouw dochter - I know your daughter (or: I am acquainted with your daughter)
Weten usually refers to knowing facts. It is often intransitive (no direct object), but can also be transitive in some cases.
- Ik weet waar je woont - I know where you live
- Ik weet dat ik het boek heb - I know that I have the book
- Ik weet het - I know (it)
In English there is no difference between "weten" and "kennen". Both are translated with "to know". Other languages differentiate like Dutch. In German, for example, you use "wissen" and "kennen" with the same meanings as the respective Dutch words. With other words you may find the reverse. For example, the Dutch "leren" could in English be "to teach" or "to learn" and they're not interchangeable in English.