In his book, Russell distinguishes several types of knowledge. He first distinguishes knowledge of truths, and of things.
"the sense in which what we know is true (...) i.e. to what are called judgements (...) may be described as knowledge of truths."
"knowledge of things (...) (is knowing) sense-data"
So I think an example of knowledge of truths would be 'This chair is brown', wheres knowledge of things would be the act of seeing the chair.
But my confusion began when he further distinguished knowledge of things into two types: knowledge of things by acquaintance and by description. Description, he explains,
"The table is 'the physical object which causes such-and-such sense-data'. This describes the table by means of the sense-data."
But I don't see why description falls under knowledge of things. Since description is a set of predicate about sense-data, not a set of sense-data itself, shouldn't description be considered as knowledge of truths? Or am I misunderstanding his terminology completely?