mIRC is capable of creating custom windows, pic windows and dialogs, all of which are explained in detail in the help file. For help with a specific dll, you should read any documentation and examples that come with it, as well as any tutorials or prior forums posts here at mirc.com about the dll.
If at this time you still dont understand it or are having trouble doing what you want to do with the dll, then just post on the forums like you have been doing so far.
