Virtual PDF printers are actually virtual drivers which install on your system and provide you with the option to print your documents to a PDF document as opposed to using physical paper. They are overall rather easy to use and involved selecting the printer to use from within the "Print" dialog.
You can use virtual PDF drivers with virtually any Windows program that has a print function. The most popular program today would probably be Microsoft Word or Microsoft Excel.
Many of these programs are Shareware (not recommended) and some of the best are actually freeware. Take your pick!