The mIRC homepage has extensive help documentation. Download and save software file into a temporary directory. Double click the mIRC exe file that is best used with your operating system. If you are using a 32 bit operating system, such as Windows 95 or Windows NT, you should run mircXXt.exe. Otherwise use the 16 bit mircXXs.exe program to install mirc.
XX refers to version number.
Start mirc from Start Menu or Program manager. Click on the IRC Servers tab. The Password field should be left blank. Now, click on Add. Click on the Identd tab.