There's not much to say, its an enclitic so its post-positional and...well...it does what it does. It conjoins things together, often in list form. I don't really see what's illogical about it.
Yes its from a PIE root, *kwe (imagine a superscript w), which is also the ancestor of the Greek te (from < Mycenaean qe) and the Sanskrit ca. In the Italic family in particular, Faliscan (Latin's closest relative) has cue, Venetic kve and Oscan and Umbrian have like a pe sound. Useless data but hopefulyl interesting more generally.
Just read a bit and internalise it, write a few sentences using it and its derivatives.
(Occasionally) Working on the following tutorials:
(P)Aristotle, Theophrastus and Peripatetic Greek
Intro Greek Poetry
Latin Historical Prose