After installing, open QuickPar and click 'Options', Copy the settings as below in the picture and press ok.
After you have download all RAR files and the first PAR2 file, open the PAR2 file to verify the downloaded files. QuickPar will start and this might be the result:
As you can see two RAR files are incomplete (Freeware Collection.part6.rar and Freeware Collection.part7.rar). The bar shows us that we need to acquire 14 more blocks before we can repair the downloaded files. Usually a couple of PAR2 files are posted together with the RAR files (in this case we've already downloaded 10 blocks) but if there aren't enough PAR2 blocks available, we have to ask the poster to create and upload more blocks. This means that you don't have to tell the poster which files are missing or incomplete, you can just say how many blocks you need.
The 'Monitor' functionality can be very handy: when you keep QuickPar activated while downloading, it will check the download directory and verify the newly downloaded files immediately. When you activate 'AutoRepair', QuickPar will start repairing as soon as enough PAR2 blocks are downloaded.
When you have downloaded enough blocks, hit the 'Repair' button to start repairing.
After QuickPar is finished, the result will be:
As you can see all files are repaired! Now it is time to extract the files using WinRAR.