The phrase "to know these things" means having information or understanding about certain facts or details.
Sentences with «to know these things»
I didn't know a thing about what it took to put together a meal. (acouplecooks.com)
There are some there now who know things are bad, but they are afraid to leave because they have been told if they do, they will get divorced. (redeeminggod.com)
She has a way of knowing things about you that you might not even admit to yourself. (thestar.com)