Change your nickname from the default by typing /nick yournickhere
You may register your nickname so no one else can you it by typing /msg nickserv register password firstname.lastname@example.org. Replace password with your password and email@example.com with your email.
The next time you log in, you will have to change to your nickname first and then identify to your nickname (tell the server that you are the owner of this nickname) by typing /msg nickserv identify password. Of course, you'll have to replace password with your password.
People with "!" or "@" in front of their names are channel operators, they have the power to kick and ban.
People with "+" in front of their names share files. You will need mIRC to download these files.