I'd like to discover the guile ecosystem. I looked at how to install a library and I didn't find a package manager, like python's pip. Does such a thing exist for guile ?
Looks like guildhall is the closest thing to pip out there. There has been some discussion on the Guile mailing lists recently around it. The posts by Wingo, Boubekki, Zaretskii, and a few others who are heavily involved with Guile development indicate a push towards making guildhall an upstream source for something called Guix that is a more general package manager intended to be independent of platform.
If you consult the Guix list of packages you will see guile there and a number of other guile related items (e.g. guile-json, guile-ncurses, etc..). I'd give that a shot. Otherwise you're on your own and you'll have to either fall back to the OS package manager or pull down the source yourself, build, and install.
Full disclosure: I haven't tried Guix myself but I've been meaning to. I'd be very interested to see how it turns out for you so if you do go this route it'd be awesome if you could provide an update with your Guix experience.
There's also been a recent call to update the libraries page and from a quick inspection there's been some small number of updates that you may find useful.