I have not seen a copy yet. However, I read accounts on them by Russell himself. He said it consists of 3 volumes, each co-author went thru the drafts in a hotel an average of 3 times. They attempted to reduce mathematics to logic. Russell mentioned about the book in his "My Philosophical Development."
Among their results: One is a class with a lone member. Zero is a class without a member. Two is a class of couples. Three is a class of triplets. There are more classes than there are things. Therefore a number is not a thing. They also developed symbolic logic. There are ways of counting other than by arithmetic
.I am writing from memory now. I would like a copy of each volume.