Once you have all the files (Part 1 through the final part) in the same folder:
You do not need to extract every part individually.
Downloading games from "repack" or "highly compressed" sites carries risks of malware or unwanted software. Always ensure your is active and consider scanning the extracted folder before running any .exe files.
Usually, all parts are listed in a numbered table at the bottom of the post.
Dealing with multi-part RAR files can be tricky because if one piece is missing or corrupted, the whole installation fails. 1. Finding the Specific Part