okay. make sure you have the latest rar, or 7zip. (7z handles rar expansion)
have all the downloaded rar archive parts in the same directory.
then highlight the first most part of that split rar archive, usually with a '.000, .001, or .rar' suffix, and using gui of 7z/rar, select 'extract here' or define custom target directory.
all the best, and welcome to the first post of your life here.