Step 1:

In mIRC, press Alt+O, this will open the mIRC Options window. On the left side, click "connect".
Enter your name and email address (doesn't have to be your real name and email though).
Enter a nickname and an alternative (this is chosen if the nickname already exists).

Step 2:

On the left, click servers. In IRC network, select Quakenet, then click the Connect to server button.

Step 3:

On the left, click Options. Mark the fields as can be seen below. Then click OK.

Now type
/join #notpron
and press enter. There you go!