Move/copy the file to ~/.irssi/scripts/autorun. Create autorun folder if does not exist. It should automatically load next time you run irssi.
Once it's loaded, do (per comments in the script):
/statusbar dccstat add dccstat
To simply connect to a secured port server:
/server -ssl irc.server.org 9999
Joins and quits can be annoying on a big channel and would have to swim through to find wanted entries. You can do "/help ignore" for other examples, but I mostly need this:
/ignore #channel JOINS PARTS QUITS