Stoat Soup webtiles is available on CKO, which is on the West side of the Atlantic; on CPO, which is in Australia; on XOM in the UK (provided by Sentei, not us); and the development version is available for console play only by ssh-ing to "crawl.montres.org.uk" (which is in the UK) using username "fortunato" and the usual ssh key used for online play (or use this key if you need a newer one - PuTTY key here).
Maybe you've been playing Crawl for years and want a complete account of the changes.
Alternatively, you just want Stoat Soup for 0.30 players, to know what might trip you up if you're used to modern vanilla DCSS.
Windows tiles builds are periodically made available for local play.
If you want to compile it yourself (the easiest way for local play on Linux), the source is available on github and the process is the same as vanilla DCSS.
Many people play Crawl online. Vanilla Crawl publishes a guide to playing online and those instructions will let you use the online servers listed above. If you want to play offline, it's easy to download the Windows build above, and it's also easy to build it yourself on Linux.
You can get a tutorial in local play, or online on crawl.montres.org.uk.
Good choice! Crawl is a very distant descendant of NetHack. There's a guide to Stoat Soup for NetHack players.
If you don't play console ("ASCII") this bit doesn't matter.
There is a convention for terminal clients that bold black text is drawn in a dark grey. Unfortunately, this convention isn't universally respected, and if you have a terminal client that gets it wrong, you won't be able to see the things Crawl draws in dark grey, including important things like walls out of your field of view.
Crawl has an option, "bold_brightens_foreground", which if it is turned off instead draws these things in blue. This looks horrible but at least you can see what you're doing. In vanilla Crawl it defaults to being turned off. In Stoat Soup, it defaults to being turned on, because watching ttyrecs with the walls dark blue gives me a headache.
So, if you have this problem where you can't see walls out of your field of view, you'll need to edit your options to set "bold_brightens_foreground = false", or fix your terminal client.