I've read that they all share some genes, internal structure, and behaviour with each other, but with different degrees of overlap depending of what the function is. E.g., archaea have some eukaryotic and some bacterial function, and eukaryotes have bacterial function in the form of mitochondria and plastids.
However I'm finding the nitty-gritty of all this rather confusing. Could anyone please explain some of the detail for me as I can't seem to make any sense of this from reading Wikipedia, etc.