Copy the certificate you made into your ~/.irssi directory:

% mv mynick.pem ~/.irssi/mynick.pem

Now, we'll add a network for DareNET, named darenet; although, you could name it anything. Just remember, the name is case-sensitive.

/network add darenet

You can add multiple servers for each network in irssi, but we only need to add one:

/server add -auto -ssl -ssl_cert ~/.irssi/mynick.pem -network darenet irc.darenet.org 6697

The next time you /connect darenet or start irssi, you'll automatically be connected to DareNET using your SSL client certificate.

Once connected, read how to add your certificate's fingerprint to N.